The COVID-19 pandemic's impact on all-cause mortality disparities in Medicare: By race, income, chronic health, mental/behavioral health, disability

BACKGROUND

The Medicare-enrolled population is heterogeneous across race, ethnicity, age, dual eligibility, and a breadth of chronic health, mental and behavioral health, and disability-related conditions, which may be differentially impacted by the COVID-19 pandemic.

OBJECTIVE

To quantify changes in all-cause mortality prior-to and in the first year of the COVID-19 pandemic across Medicare's different sociodemographic and health-condition subpopulations.

METHODS

This observational, population-based study used stratified bivariate regression to investigate Medicare fee-for-service subpopulation differences in pre-pandemic (i.e., 2019 versus 2016) and pandemic-related (2020 versus 2019) changes in all-cause mortality.

RESULTS

All-cause mortality in the combined Medicare-Advantage (i.e., managed care) and fee-for-service beneficiary population improved by a relative 1% in the ten years that preceded the COVID-19 pandemic, but then escalated by a relative 15.9% in 2020, the pandemic's first year. However, a closer look at Medicare's fee-for-service subpopulations reveals critical differences. All-cause mortality had actually been worsening prior to the pandemic among most psychiatric and disability-related condition groups, all race and ethnicity groups except White Non-Hispanic, and Medicare-Medicaid dual-eligible (i.e., low-income) beneficiaries. Many of these groups then experienced all-cause mortality spikes in 2020 that were over twice that of the overall Medicare fee-for-service population. Of all 61 chronic health conditions studied, beneficiaries with schizophrenia were the most adversely affected, with all-cause mortality increasing 38.4% between 2019 and 2020.

CONCLUSION

This analysis reveals subpopulation differences in all-cause mortality trends, both prior to and in year-one of the COVID-19 pandemic, indicating that the events of 2020 exacerbated preexisting health-related inequities.

Diabetes prevention and the role of risk factor reduction in the Medicare population

Medicare is keenly aware of the secular changes in weight gain and of the nearly parallel increases in both the incidence and prevalence of type 2 diabetes throughout the U.S. population. The Medicare population, however, differs from the population at large because of its advanced age and frequency of comorbid conditions and/or disability. These factors affect life span as well as participation in and potential benefit from lifestyle modification and risk-factor reduction activities. Further, macrovascular disease is the greatest burden for older beneficiaries with diabetes, and its risks may antedate the appearance of hyperglycemia. Both diabetes prevention and treatment must be considered in this context. Medicare benefits focus on reduction of cardiovascular risk and mitigation of more temporally immediate complications of weight gain and glucose elevation. These preventive services and interventions are described.

A survey of reports of quetiapine-associated hyperglycemia and diabetes mellitus

OBJECTIVE

To explore the clinical characteristics of hyperglycemia in patients treated with quetiapine.

METHOD

A pharmacovigilance survey of spontaneously reported adverse events in quetiapine-treated patients was conducted using reports from the U.S. Food and Drug Administration MedWatch program (January 1, 1997, through July 31, 2002) and published cases using the search terms hyperglycemia, diabetes, acidosis, ketosis, and ketoacidosis.

RESULTS

We identified 46 reports of quetiapine-associated hyperglycemia or diabetes and 9 additional reports of acidosis that occurred in the absence of hyperglycemia and were excluded from the immediate analyses. Of the reports of quetiapine-associated hyperglycemia, 34 patients had newly diagnosed hyperglycemia, 8 had exacerbation of preexisting diabetes mellitus, and 4 could not be classified. The mean +/- SD age was 35.3 +/- 16.2 years (range, 5-76 years). New-onset patients (aged 31.2 +/- 14.8 years) tended to be younger than those with preexisting diabetes (43.5 +/- 16.4 years, p = .08). The overall male:female ratio was 1.9. Most cases appeared within 6 months of quetiapine initiation. The severity of cases ranged from mild glucose intolerance to diabetic ketoacidosis or hyperosmolar coma. There were 21 cases of ketoacidosis or ketosis. There were 11 deaths.

CONCLUSION

Atypical antipsychotic use may unmask or precipitate hyperglycemia.

UPDATE

An additional 23 cases were identified since August 1, 2002, the end of the first survey, by extending the search through November 30, 2003, bringing the total to 69.

Pancreatitis associated with atypical antipsychotics: from the Food and Drug Administration's MedWatch surveillance system and published reports

STUDY OBJECTIVE

To investigate the relative numbers and clinical characteristics of pancreatitis in patients treated with the atypical antipsychotic agents, clozapine, olanzapine, and risperidone, versus the conventional neuroleptic, haloperidol.

DESIGN

Pharmacovigilance study of pooled, spontaneously reported adverse events.

SETTING

Government-affiliated drug evaluation center.

PATIENTS

One hundred ninety-two patients who developed pancreatitis during treatment with one or more antipsychotic agents.

INTERVENTION

Patients were identified with the Food and Drug Administration's MedWatch surveillance program and a MEDLINE search.

MEASUREMENTS AND MAIN RESULTS

Most cases of pancreatitis occurred within 6 months after the start of therapy with one or more antipsychotic agents. Of the reports of pancreatitis occurring in conjunction with these drugs, 40%, 33%, 16%, and 12% were in patients receiving treatment with clozapine, olanzapine, risperidone, and haloperidol, respectively. In 50% of the patients receiving haloperidol, an atypical antipsychotic was listed as a concomitant drug. Valproate was administered concomitantly in 23% of patients. Hyperglycemia and acidosis, although uncommon, developed with all the drugs except haloperidol. Twenty-two patients died. In contrast to patients who developed pancreatitis while receiving an atypical antipsychotic, those who developed the disease while receiving haloperidol were women and tended to be older.

CONCLUSION

The number of reports involving the three atypical antipsychotic agents and the relative paucity of reports involving haloperidol, despite its more extensive patient exposure, suggest that atypical antipsychotics may precipitate pancreatitis. However, the risk may not be the same with all agents; pancreatitis was reported most frequently with clozapine, followed by olanzapine, and then risperidone. The temporal relationship of the onset of pancreatitis with the start of drug therapy further supports a cause-and-effect relationship.

Risperidone-associated diabetes mellitus: a pharmacovigilance study

STUDY OBJECTIVE

To explore the clinical characteristics of hyperglycemia in patients treated with risperidone.

DESIGN

Pharmacovigilance survey of spontaneously reported adverse events in risperidone-treated patients, with reports of haloperidol-associated hyperglycemia used as a control.

SETTING

Government-affiliated drug evaluation center.

INTERVENTION

The Food and Drug Administration MedWatch surveillance program was queried (risperidone, 1993-February 2002; haloperidol, late 1970s-February 2002) and results pooled with published cases.

MEASUREMENTS AND MAIN RESULTS

We identified 131 reports of risperidone-associated hyperglycemia in addition to seven reports of patients with hyperglycemia who received combined risperidone-haloperidol therapy and six reports of acidosis that occurred in the absence of hyperglycemia. We found 13 reports of haloperidol-associated hyperglycemia and 11 reports of acidosis without hyperglycemia. Of the reports of risperidone-associated hyperglycemia (monotherapy), 78 patients had newly diagnosed hyperglycemia, 46 had exacerbated preexisting diabetes, and 7 could not be classified. Mean +/- SD age was 39.8 +/- 17.4 years (range 8-96 yrs). Patients with new-onset diabetes (mean +/- SD age 34.8 +/- 15.7 yrs) were younger than those with preexisting diabetes (mean +/- SD age 48.8 +/- 17.5 yrs). The overall male:female ratio was 1.5. In most patients, hyperglycemia appeared within 3 months of the start of risperidone therapy. Severity of disease ranged from mild glucose intolerance to diabetic ketoacidosis or hyperosmolar coma. Twenty-six patients with acidosis or ketosis were reported. Four patients died.

CONCLUSION

Atypical antipsychotic treatment may unmask or precipitate hyperglycemia. Although such cases attributed to clozapine or olanzapine are more numerous than those associated with risperidone, the number for risperidone-associated hyperglycemia is relatively higher than that observed with the conventional neuroleptic haloperidol.

Olanzapine-associated diabetes mellitus

STUDY OBJECTIVE

To explore the clinical characteristics of hyperglycemia in patients treated with olanzapine.

DESIGN

Retrospective, epidemiologic survey of spontaneously reported adverse events related to olanzapine therapy

SETTING

Government-affiliated drug evaluation center.

PATIENTS

Two hundred thirty-seven patients with olanzapine-associated diabetes or hyperglycemia.

INTERVENTION

One hundred ninety-six cases from January 1994-May 15, 2001, were identified with the United States Food and Drug Administration's MedWatch Drug Surveillance System, and 41 cases published through May 15, 2001, were identified with MEDLINE or through meeting abstracts.

MEASUREMENTS AND MAIN RESULTS

Of the 237 cases, 188 were new-onset diabetes, 44 were exacerbations of preexistent disease, and 5 could not be classified. Mean patient age for newly diagnosed cases was 40.7+/-12.9 years and male:female ratio was 1.8. Seventy-three percent of all cases of hyperglycemia appeared within 6 months of start of olanzapine therapy. Eighty patients had metabolic acidosis or ketosis, 41 had glucose levels of 1000 mg/dl or greater, and 15 patients died. When olanzapine was discontinued or the dosage decreased, 78% of patients had improved glycemic control. Hyperglycemia recurred in 8 of 10 cases with rechallenge.

CONCLUSIONS

Number of reports, temporal relationship to start of olanzapine therapy, relatively young age, and improvement on drug withdrawal suggest that olanzapine may precipitate or unmask diabetes in susceptible patients.

Increased myocardial blood flow during acute exposure to simulated altitudes

BACKGROUND

Although only poor data exist on changes in myocardial blood flow (MBF) under acute hypoxia, patients with known coronary artery disease are advised not to exceed a moderate altitude exposure of about 2000 m above sea level.

METHODS AND RESULTS

We measured MBF with positron emission tomography using O-15--labeled water in 8 healthy human volunteers (aged 26 +/- 3 years [mean +/- SD]) at baseline (450 m above sea level, Zurich, Switzerland) and during acute hypoxic hypoxemia induced by inhalation of 2 hypoxic gas mixtures corresponding to altitudes of 2000 and 4500 m. MBF remained unchanged at 2000 m (increase of 10%, not significant) but increased significantly at 4500 m (62%, P <.001), exceeding the relative increase in rate pressure product.

CONCLUSIONS

Our results may explain why exposure to an altitude of 2000 m (corresponding to the cabin pressure in most airplanes during flight) is clinically well tolerated, even by patients with reduced coronary flow reserve, such as those with coronary artery disease. However, at an altitude of 4500 m, MBF increases significantly, supporting the recommendation that patients with impaired flow reserve avoid exposure to higher altitudes.

Effects of hypobaric hypoxia on vascular endothelial growth factor and the acute phase response in subjects who are susceptible to high-altitude pulmonary oedema

In order to investigate whether vascular endothelial growth factor (VEGF) and inflammatory pathways are activated during acute hypobaric hypoxia in subjects who are susceptible to high-altitude pulmonary oedema (HAPE-S), seven HAPE-S and five control subjects were exposed to simulated altitude corresponding to 4000 m in a hypobaric chamber for 1 day. Peripheral venous blood was taken at 450 m (Zürich level) and at 4000 m, and levels of erythropoietin (EPO), VEGF, interleukin-6 (IL-6) and the acute-phase proteins complement C3 (C3), alpha1-antitrypsin (alpha1AT), transferrin (Tf) and C-reactive protein (CRP) were measured. Peripheral arterial oxygen saturation (SaO2) was recorded. Chest radiography was performed before and immediately after the experiment. EPO increased during altitude exposure, correlating with SaO2, in both groups (r = -0.86, P < 0.001). Venous serum VEGF did not show any elevation despite a marked decrease in SaO2 in the HAPE-S subjects [mean (SD) HAPE-S: 69.6 (9.1)%; controls: 78.7 (5.2)%]. C3 and alpha1AT levels increased in HAPE-S during hypobaric hypoxia [from 0.94 (0.11) g/l to 1.07 (0.13) g/l, and from 1.16 (0.08) g/l to 1.49 (0.27) g/l, respectively; P < 0.05], but remained within the clinical reference ranges. No significant elevations of IL-6, Tf or CRP were observed in either group. The post-exposure chest radiography revealed no signs of oedema. We conclude that VEGF is not up-regulated in HAPE-S and thus does not seem to increase critically pulmonary vascular permeability during the 1st day at high altitude. Furthermore, our data provide evidence against a clinically relevant inflammation in the initial phase of exposure to hypoxia in HAPE-S, although C3 and alpha1AT are mildly induced.

Papillary and follicular thyroid carcinoma metastatic to the skin: a case report and review of the literature

Cutaneous metastases from thyroid cancers are rare. We report the case of an otherwise asymptomatic 81-year-old woman with an enlarging scalp lesion. Her solitary skin metastasis was the presenting feature of thyroid carcinoma. Routine histopathology of the lesion was notable for an atypical clear cell neoplasm. Immunohistochemistry was positive for thyroglobulin. Subsequent resection of the thyroid gland identified separate foci (< 1 cm) for both papillary and follicular carcinoma. Although such immunohistochemical staining has been used previously, it has never been reported to provide the definitive diagnosis for a solitary cutaneous metastasis from the thyroid. Previous tumors had anatomic features in a clinical context that permitted identification by routine light microscopy. Clear cell features found in the follicular focus of carcinoma in the thyroid suggest that it is the primary. A worldwide literature review reveals that follicular carcinoma has a greater preponderance than papillary carcinoma for cutaneous metastasis and that the majority of skin metastases from either papillary or follicular thyroid cancer are localized to the head and neck.

Changes of cerebral blood flow during short-term exposure to normobaric hypoxia

Decreased arterial partial oxygen pressure (PaO2) below a certain level presents a strong stimulus for increasing cerebral blood flow. Although several field studies examined the time course of global cerebral blood flow (gCBF) changes during hypoxia at high altitude, little was known about the regional differences in the flow pattern. Positron emission tomography (PET) with [(15)O]H2O was used on eight healthy volunteers to assess regional cerebral blood flow (rCBF) during short-term exposure to hypoxia corresponding to simulated altitudes of 3,000 and 4,500 m. Scans at the simulated altitudes were preceded and followed by baseline scans at the altitude of Zurich (450 m, baseline-1 and baseline-2). Each altitude stage lasted 20 minutes. From baseline to 4,500 m, gCBF increased from 34.4 +/- 5.9 to 41.6 +/- 9.0 mL x minute(-1) x 100 g(-1) (mean +/- SD), whereas no significant change was noted at 3,000 m. During baseline-2 the flow values returned to those of baseline-1. Statistical parametric mapping identified the hypothalamus as the only region with excessively increased blood flow at 4,500 m (+32.8% +/- 21.9% relative to baseline-1). The corresponding value for the thalamus, the structure with the second largest increase, was 19.2% +/- 16.3%. Compared with the rest of the brain, an excessive increase of blood flow during acute exposure to hypoxia is found in the hypothalamus. The functional implications are at present unclear. Further studies of this finding should elucidate its meaning and especially focus on a potential association with the symptoms of acute mountain sickness.

Retinal changes mimicking diabetic retinopathy in two nondiabetic, growth hormone-treated patients

A role for GH in the pathogenesis of diabetic retinopathy has long been postulated. Previous clinical studies, however, have been confounded by hyperglycemia. We have identified 2 cases of retinopathy associated with exogenous GH therapy in nondiabetic patients. Cases were identified through the MedWatch drug surveillance system of the U.S. Food and Drug Administration. Causality by concomitant medications was excluded by a search of the literature and the FDA data base. The first patient, an obese, 31-yr-old male with traumatic hypothalamic injury, presented with nonproliferative retinopathy and macular edema, resulting in decreased visual acuity (OD 20/40-1; OS count fingers), which required laser surgery. Human GH had been initiated at 0.009 mg/ kg.day, 14 months earlier, and titrated to 0.017 mg/kg.day. The second patient, a nonobese, 11-yr-old girl receiving GH for the management of short stature in Turner's Syndrome, presented with neovascularization. GH doses were 0.033 mg/kg.day for the first 17 months and 0.043 mg/ kg.day for the following 5 months. Cumulative laboratory and clinical observations suggest that GH and related peptides have a role in retinal pathology independent of the degree of glucose tolerance.

A Possible Pre-Zollinger-Ellison State: Report on a Novel Lesion

OBJECTIVE

To describe a patient with a potential harbinger of Zollinger-Ellison syndrome.

METHODS

We present a case of a 29-year-old woman with persistent galactorrhea and gastric distress, who was a member of an extensive multiple endocrine neoplasia (MEN) I kindred. Both clinical and laboratory findings are reviewed.

RESULTS

Laboratory studies were notable for persistent hypercalcemia and increased levels of parathyroid hormone and fasting pancreatic polypeptide. Because of nonspecific upper gastrointestinal distress, which was sometimes responsive to antacids, the patient underwent further diagnostic evaluation. Baseline gastrin levels were normal. A secretin challenge test yielded normal results. At upper endoscopy, visual findings in the stomach and duodenum were unremarkable. A raised nodule (4 by 2 by 2 mm) was removed from an otherwise normal-appearing duodenum as a routine biopsy procedure. The acinar architecture, the inconspicuous nucleoli, and the granular, eosinophilic cytoplasm of the cells were diagnostic of a neuroendocrine tumor. Histologic immunohistochemical staining was positive for gastrin but negative for pancreatic polypeptide. RNA studies were not technically possible. Subsequently, serum pancreatic polypeptide levels normalized. The patient ultimately had hyperplastic parathyroid glands resected.

CONCLUSION

The duodenal lesion may be a very early gastrinoma, a preclinical manifestation of the Zollinger-Ellison syndrome. The role of early resection of such lesions remains to be determined.

Papilledema in 15 renally compromised patients treated with growth hormone

Intracranial hypertension with papilledema has been reported in renal patients, but a survey of the literature suggests that the incidence rate is low. We present reports of 15 of approximately 1,670 patients with renal disorders, who were treated with growth hormone for impaired growth and subsequently developed symptoms and/or signs of intracranial hypertension. The male:female ratio was 6.5:1, and the median age was 12 years. The median duration of growth hormone treatment before onset of symptoms or signs was 13 weeks. All but 2 patients were symptomatic. In the patients in whom growth hormone therapy is known to have been discontinued, the symptoms and signs of intracranial hypertension abated. At least 4 of these patients experienced a recurrence when re-exposed to growth hormone. Many of the affected patients presented with predisposing conditions, but growth hormone appears to have been the precipitating factor. Prospective funduscopic evaluation may be warranted in patients with renal disorders who are receiving growth hormone.

Effect of exercise-induced hyperventilation on airway resistance and cycling endurance

The purpose of the present study was to investigate the effect of exercise induced hyperventilation and hypocapnia on airway resistance (Raw), and to try to answer the question whether a reduction of Raw is a mechanism contributing to the increase of endurance time associated with a reduction of exercise induced hyperventilation as for example has been observed after respiratory training. Eight healthy volunteers of both sexes participated in the study. Cycling endurance tests (CET) at 223 (SD 47) W, i.e. at 74 (SD 5)% of the subject's peak exercise intensity, breathing endurance tests and body plethysmograph measurements of pre- and postexercise Raw were carried out before and after a 4-week period of respiratory training. In one of the two CET before the respiratory training CO2 was added to the inspired air to keep its end-tidal concentration at 5.4% to avoid hyperventilatory hypocapnia (CO2-test); the other test was the control. The pre-exercise values of specific expiratory Raw were 8.1 (SD 2.8), 6.8 (SD 2.6) and 8.0 (SD 2.1) cm H2O.s and the postexercise values were 8.5 (SD 2.6), 7.4 (SD 1.9) and 8.0 (SD 2.7) cm H2O.s for control CET, CO2-CET and CET after respiratory training, respectively, all differences between these tests being nonsignificant. The respiratory training significantly increased the respiratory endurance time during breathing of 70% of maximal voluntary ventilation from 5.8 (SD 2.9) min to 26.7 (SD 12.5) min. Mean values of the cycling endurance time (tcend) were 22.7 (SD 6.5) min in the control, 19.4 (SD 5.4) min in the CO2-test and 18.4 (SD 6.0) min after respiratory training. Mean values of ventilation (VE) during the last 3 min of CET were 123 (SD 35.8) l.min-1 in the control, 133.5 (SD 35.1) l.min-1 in the CO2-test and 130.9 (SD 29.1) l.min-1 after respiratory training. In fact, six subjects ventilated more and cycled for a shorter time, whereas two subjects ventilated less and cycled for a longer time after the respiratory training than in the control CET. In general, the subjects cycled longer the lower the VE, if all three CET are compared. It is concluded that Raw measured immediately after exercise is independent of exercise-induced hyperventilation and hypocapnia and is probably not involved in limiting tcend, and that tcend at a given exercise intensity is shorter when VE is higher, no matter whether the higher VE occurs before or after respiratory training or after CO2 inhalation.

Volume changes in the forearm and lower limbs during 2 h of acute hypobaric hypoxia in nonacclimatized subjects

To investigate the role of fluid shifts during the short-term adjustment to acute hypobaric hypoxia (AHH), the changes in lower limb (LV) and forearm volumes (FV) were measured using a strain-gauge plethysmograph technique in ten healthy volunteers exposed to different altitudes (450 m, 2500 m, 3500 m, 4500 m) in a hypobaric chamber. Arterial blood pressure, heart rate, arterial oxygen saturation (SaO2), endtidal gases, minute ventilation and urine flow were also determined. A control experiment was performed with an analogous protocol under normobaric normoxic conditions. The results showed mean decreases both in LV and FV of 0.52 (SD 0.39) ml x 100 ml(-1) and -0.65 (SD 0.32) ml x 100 ml(-1), respectively, in the hypoxia experiments [controls: LV 0.28 (SD 0.37), FV 0.41 (SD 0.47) ml x 100 ml(-1)]. Descent to normoxia resulted in further small but not significant decreases in mean LV [-0.02 (SD 0.11) ml x 100 ml(-1)], whereas mean FV tended to increase slightly [ + 0.02 (SD 0.14) ml x 100 ml(-1)]; in the control experiments mean LV and FV decreased continuously during the corresponding times [-0.19 (SD 0.31), -0.18 (SD 0.10) ml x 100 ml(-1) , respectively]. During the whole AHH, mean urine flow increased significantly from 0.84 (SD 0.41) ml x min(-1) to 3.29 (SD 1.43) ml x min(-1) in contrast to the control conditions. We concluded that peripheral fluid volume shifts form a part of the hypoxia-induced acute cardiovascular changes at high altitude. In contrast to the often reported formation of peripheral oedema after prolonged exposure to hypobaric hypoxia, the results provided no evidence for the development of peripheral oedema during acute induction to high altitude. However, the marked increase in interindividual variance in SaO2 and urine flow points to the appearance of the first differences in the short-term adjustment even after 2 h of acute hypobaric hypoxia.

Heterogeneous activity of pulmonary vagal receptors during high-frequency oscillation ventilation

The purpose of the study was to examine the response of vagal pulmonary slowly adapting stretch receptors (SAR) to high-frequency oscillation ventilation (HFO) in rabbits by analyzing the afferent activity recorded in vagal single-fiber preparations. The vagal afferent activity was recorded during short runs of HFO with a stroke volume of 2-3 ml/kg applied at oscillation frequencies (fosc) of 5, 10, 15, 20, and 25 Hz and each frequency at three levels of mean airway pressure (P(aw)), namely, 1, 3, and 8 cm H2O. The receptor discharge rates during HFO were compared with those during quiet spontaneous breathing as well as during static lung inflations and deflations. The majority of SAR was stimulated by HFO, however, the SAR discharge patterns during HFO were less homogeneous than during static lung inflations. The heterogeneity of SAR responses to HFO became pronounced with increasing P(aw) and fosc. From the results, we conclude that HFO elicits heterogeneous discharge patterns of SAR, but the previously reported heterogeneity of responses of rapidly adapting receptors was even greater. This heterogeneity of vagal activity is probably the result of heterogeneous mechanical conditions within the lungs during HFO and may, in turn, give rise to the various types of respiratory reflex responses to HFO.

Running training and co-ordination between breathing and running rhythms during aerobic and anaerobic conditions in humans

The study was carried out on ten triathletes, six sprinters and ten subjects not trained in running (controls) to assess the effects of training history on the co-ordination between breathing and running rhythms during running on a treadmill. Three exercise intensities were used: 50%, 80% and 110% of the subject's anaerobic threshold (AT). All three intensities were performed twice: once with spontaneous breathing and once with breathing intentionally co-ordinated to the running rhythm. Heart rate, respiratory parameters and leg movements were continuously recorded. Blood lactate concentrations were measured discontinuously. The degree of co-ordination between running and breathing was quantified as the percentage of inspirations and/or expirations starting during the same phase of step. The results showed that the degree of both spontaneous and intended co-ordination at aerobic exercise intensities was in all three groups the same and increased in all groups with increasing intensity from 50% to 80% of AT; further increase of intensity to 110% of AT was associated with a significant decrease of co-ordination in controls and sprinters, whereas triathletes were able to maintain the same high degree of co-ordination as at 80% of AT. It was concluded that running training of either type at aerobic work loads had no effect on the co-ordination between running and breathing rhythms. At anaerobic intensities, however, the degree of co-ordination between running and breathing rhythms was higher in the endurance trained athletes than in the sprinters or in the untrained subjects. The degree of co-ordination increased with increasing regularity of breathing.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical respiratory system input impedance during high-frequency oscillatory ventilation in rabbits

OBJECTIVES

To study the mechanical properties of the rabbit respiratory system during high-frequency oscillatory ventilation by means of mechanical respiratory impedance measurement and to characterize the changes in oscillation mechanics of the respiratory system occurring after bilateral vagotomy.

DESIGN

Acute experimental trial.

SETTING

Physiology laboratory.

SUBJECTS

Ten adult rabbits (mean body weight 3.1 kg).

MEASUREMENTS AND MAIN RESULTS

Anesthetized rabbits were exposed to short runs of high-frequency oscillatory ventilation, with stroke volumes of 5.0, 6.6, and 10.0 mL, applied at oscillation frequencies of 10, 15, 20, and 25 Hz before and after vagotomy. Mechanical respiratory input impedance was determined from the pressure and flow signals simultaneously measured at the airway opening and analyzed in terms of its real and imaginary parts. (The real part of respiratory impedance characterizes the resistive property of the lungs and chest wall; the imaginary part of respiratory impedance characterizes the elastic and inertial properties of the lungs and chest wall.) At all stroke volumes and oscillation frequencies studied, vagotomy resulted in a decrease in the real part of respiratory impedance. After vagotomy, the real part of respiratory impedance was stroke volume-independent, and exhibited negative frequency dependency. Vagotomy also led to a decrease in the imaginary part of respiratory impedance, mainly at lower oscillation frequencies, and thus, to a higher resonant frequency of the respiratory system.

CONCLUSIONS

Mechanical respiratory impedance measurement proved to be a useful method to study the mechanical properties of the respiratory system during high-frequency oscillatory ventilation. The results suggest that vagally mediated reflex changes in respiratory system mechanics are associated with high-frequency oscillatory ventilation, depending on the ventilatory variables that are used.

The effects of acute altitude exposure in Swiss highlanders and lowlanders

The functional characteristics at rest in responding to stepwise acute exposure to simulated altitude (6000 m) were compared in 10 acclimatized mountaineers (highlanders), residents of Zermatt (1616 m) working at an altitude up to about 4000 m, and in 11 nonacclimatized control subjects (lowlanders) living and working in Zurich (450 m). In comparison with the lowlanders, the highlanders showed at altitude significantly greater hyperventilation, lower heart rate and systolic blood pressure, smaller haemoconcentration, lower urodilatin secretion and natriuresis, and a preserved neuropsychological ability (attentiveness) and vasomotor tone (diastolic blood pressure); the critical altitude at which hypoxic short-term adaptation became insufficient was 6000 m. The lowlanders, however, manifested reduced tolerance of hypoxia, i.e. insufficient short-term adjustment with subjective and objective distress coinciding with the first signs of hypoxia of the central nervous system, already apparent at and above 4000 m. It was concluded that the functional differences between highlanders and lowlanders in responding to acute gradual hypoxia indicated factors contributing to altitude acclimatization.

Discharge of pulmonary rapidly adapting stretch receptors during HFO ventilation

High-frequency oscillatory ventilation (HFOV) has been shown to stimulate slowly adapting pulmonary stretch receptors (PSR) and thereby to inhibit spontaneous breathing, i.e. HFOV prolongs expiration or even elicits normocapnic apnea. However, during HFOV respiratory effects possibly mediated by pulmonary rapidly adapting receptors (RAR) have also been observed, e.g., diaphragmatic activation or augmented breaths. Therefore, we analyzed HFOV-induced changes in RAR activity in anaesthetized rabbits by mean of single fibre preparations of vagal RAR afferents. HFOV was applied in several combinations of airway pressure (Paw) and oscillation frequency (fOsc). In the sample of 60 RAR fibres prepared in 20 rabbits we found a wide spectrum of discharge patterns during HFOV. The inspiratory discharge rate during HFOV was increased in 38, decreased in 10, and unchanged in 12 RAR. The expiratory discharge rate was increased in 34, decreased in 17, and unchanged in 9 RAR. The effects of gradually changing Paw or of fOsc during HFOV were different in different fibres. In 17 fibres both inspiratory and expiratory discharge rates rose with increasing Paw during HFOV, whereas 19 fibres were not affected by increasing Paw. In some fibres either the inspiratory (12) or the expiratory (9) activity was inhibited in proportion to increasing Paw. From these results we conclude, that (a) the changes of RAR activity during HFOV are heterogeneous and the reflex effects of RAR stimulation may be balanced by RAR with decreased activity; (b) this heterogeneity of RAR discharge patterns explains the dominancy in the control of breathing during HFOV of the homogeneously stimulated PSR; and (c) depending on HFOV ventilatory parameters used the overall RAR stimulation may be strong enough to overrule the inspiration-inhibiting effects of PSR.

Reflex apnea induced by high-frequency oscillatory ventilation in rabbits

In rabbits with intact vagus nerves, HFOV applied for 10-20 s caused apnea (i.e., respiratory arrest for as long as HFOV lasted) accompanied by tonic discharges of the diaphragm. To identify the vagal mechanisms involved in this type of apnea, the vagus nerves of anaesthetized rabbits were gradually cooled from 37 degrees C to 0 degree C, i.e., the vagal fibres were, corresponding to their diameter, successively blocked. At each temperature, the effects of HFOV on spontaneous breathing were compared with those of static lung inflation and deflation: Between 20 degrees C and 14 degrees C, the lung inflation reflex (mediated by pulmonary slowly adapting stretch receptors = PSR) was weakened or abolished, whereas the lung deflation reflex (mediated by rapidly adapting stretch receptors = RAR) was reinforced; the HFOV-induced apnea occurred less frequently, however, the accompanying diaphragmatic activity was enhanced. Between 14 degrees C and 5 degrees C, both HFOV and large static inflation caused a slight increase of breathing frequency in the majority of animals. Some animals, however, responded even below 14 degrees C by apnea to both HFOV and inflation, and, under these conditions, both HFOV- and inflation-induced apnea were accompanied by a pronounced tonic diaphragmatic activity. At 5 degrees C, the effects of HFOV as well as of inflation (except in two animals) and deflation were abolished. From the results we conclude that in rabbits the apnea during HFOV is mainly mediated by stimulation of PSR, and the concomitant tonic activity of the diaphragm is mainly due to stimulation of RAR, as it is reinforced with gradual blockade of PSR fibres and abolished when only non-myelinated fibres are intact.

[Is altitude good for health?]

Health at altitude depends on the success of functional adjustments. Only the success of the short-term adjustments including increased tidal volume, acceleration of circulation, centralization of blood volume, hemoconcentration and adjustment of de diuresis to reduce cardiac volume overload render acclimatization possible. During these long-term adjustments, which always remain incomplete at altitudes above 2000 to 3000 m, mainly the cardiovascular economy and the respiratory efficiency are improved. Failure of the short-term adjustments excludes acclimatization and may be due to reduced physical capacity or to excessive physical activity (too fast too high). It is associated with sympathetic cardiac volume overload, central hypoxia, antidiuresis and distress which result in acute mountain sickness. Health at altitude may be preserved by moderating the ascent, the duration and the physical activity there.

Respiratory, circulatory and neuropsychological responses to acute hypoxia in acclimatized and non-acclimatized subjects

Respiratory, circulatory and neuropsychological responses to stepwise, acute exposure at rest to simulated altitude (6,000 m) were compared in ten acclimatized recumbent mountaineers 24 days, SD 11 after descending from Himalayan altitudes of at least 4,000 m with those found in ten non-acclimatized recumbent volunteers. The results showed that hypoxic hyperpnoea and O2 consumption at high altitudes were significantly lower in the mountaineers, their alveolar gases being, however, similar to those of the control group. In the acclimatized subjects the activation of the cardiovascular system was less marked, systolic blood pressure, pulse pressure, heart rate and thus (calculated) cardiac output being always lower than in the controls; diastolic blood pressure and peripheral vascular resistance, however, were maintained throughout in contrast to the vasomotor depression induced by central hypoxia which occurred in the non-acclimatized subjects at and above 4,000 m [alveolar partial pressure of O2 less than 55-50 mmHg (7.3-6.6 kPa)]. It was concluded that in the acclimatized subjects at high altitude arterial vasodilatation and neurobehavioural impairment, which in the non-acclimatized subjects reflect hypoxia of the central nervous system, were prevented; that acclimatization to high altitude resulted in a significant improvement of respiratory efficiency and cardiac economy, and that maintaining diastolic blood pressure (arterial resistance) at and above 4,000 m may represent a useful criterion for assessing hypoxia acclimatization.

Altitude diuresis: endocrine and renal responses to acute hypoxia of acclimatized and non-acclimatized subjects

As a result of our recently published studies we have thought that altitude diuresis resulting from hypoxic stimulation of the arterial chemoreceptors reduces the cardiac volume overload. To test this hypothesis, cardiovascular, endocrine and renal responses to stepwise acute exposure to simulated altitude (6,000 m) were compared in ten acclimatized recumbent mountaineers a mean of 24 days, SD 11, after descending from Himalayan altitudes of at least 4,000 m, with those found in ten non-acclimatized recumbent volunteers. The results showed that natriuresis and diuresis typified the renal responses to altitude exposure of both the acclimatized as well as non-acclimatized subjects, as long as altitude was well tolerated. It was concluded that the renal effects were mediated by atrial natriuretic peptide release and slight suppression of arginine-vasopressin (AVP) secretion, that the increased urine flow at altitude offset the cardiac (volume) overload resulting from hypoxic stimulation of the arterial chemoreceptors, and that enhanced AVP secretion, as found in the non-acclimatized subjects at and above 4,000 m, coincided with subjective and objective distress, i.e. with inadequate altitude adjustment owing to insufficient chemoreflex effects and central hypoxia.

Circadian rhythms of specific airway conductance and bronchial reactivity to histamine: the effects of parasympathetic blockade

In ten healthy, nonsmoking, non-atopic, young volunteers, specific airway conductance and bronchial response to aerosolized histamine were measured plethysmographically at intervals of 4.8 h during two periods of 24 h, i.e. one day without, the other with, a parasympatholytic aerosol (0.20-0.24 mg ipratropium bromide) inhaled 1 h before each measurement, in order to determine the role of the parasympathetic innervation in the circadian rhythms of the airways. Specific airway conductance and bronchial reactivity showed clear circadian variations with corresponding peak times (16.11 and 04.41 h, respectively). Topical vagal blockade markedly increased specific conductance and resulted in a significant reduction of its rhythm amplitude, whereby the strong correlation between specific conductance and heart rate was significantly diminished. On the other hand, bronchial reactivity to histamine was lowered without flattening of its circadian rhythm. It is concluded that central parasympathetic outflow is an essential factor for the circadian rhythm of bronchial tone and, thus, for the increase in bronchial resistance at night.

Circadian rhythms of specific airway conductance and bronchial reactivity to histamine: the effects of parasympathetic blockade

In ten healthy, nonsmoking, non-atopic, young volunteers, specific airway conductance and bronchial response to aerosolized histamine were measured plethysmographically at intervals of 4.8 h during two periods of 24 h, i.e. one day without, the other with, a parasympatholytic aerosol (0.20-0.24 mg ipratropium bromide) inhaled 1 h before each measurement, in order to determine the role of the parasympathetic innervation in the circadian rhythms of the airways. Specific airway conductance and bronchial reactivity showed clear circadian variations with corresponding peak times (16.11 and 04.41 h, respectively). Topical vagal blockade markedly increased specific conductance and resulted in a significant reduction of its rhythm amplitude, whereby the strong correlation between specific conductance and heart rate was significantly diminished. On the other hand, bronchial reactivity to histamine was lowered without flattening of its circadian rhythm. It is concluded that central parasympathetic outflow is an essential factor for the circadian rhythm of bronchial tone and, thus, for the increase in bronchial resistance at night.

Location of pulmonary stretch receptors in the guinea-pig

The site of pulmonary slowly adapting stretch receptors (SRs) was investigated in anaesthetized, thoracotomized and artificially ventilated guinea-pigs. The location of SRs within the lungs and airways was determined by analyzing the changes of SR single fibres discharge patterns in response to (a) occlusion of the airways, (b) local probing, and (c) microinjection of the non-diffusible local anaesthetic cinchocaine into the presumed receptor site. The great majority (92%) of the 79 SRs examined was localized in small airways or in lung parenchyma ('peripheral SRs'), whereas only 8% were located in large airways, i.e., in the trachea, main bronchi and lobar bronchi ('central SRs'). The discharge responses to lung inflation and to ammonia inhalation slightly differed between these two SR groups. With the pronounced prevalence of peripheral SRs, the guinea-pig seems to take a unique position among the species examined hitherto.

Rate of erythropoietin formation in humans in response to acute hypobaric hypoxia

This study was carried out to investigate the early changes in erythropoietin (EPO) formation in humans in response to hypoxia. Six volunteers were exposed to simulated altitudes of 3,000 and 4,000 m in a decompression chamber for 5.5 h. EPO was measured by radioimmunoassay in serum samples withdrawn every 30 min during altitude exposure and also in two subjects after termination of hypoxia (4,000 m). EPO levels during hypoxia were significantly elevated after 114 and 84 min (3,000 and 4,000 m), rising thereafter continuously for the period investigated. Mean values increased from 16.0 to 22.5 mU/ml (3,000 m) and from 16.7 to 28.0 mU/ml (4,000 m). This rise in EPO levels corresponds to 1.8-fold (3,000 m) and 3.0-fold (4,000 m) increases in the calculated production rate of the hormone. After termination of hypoxia, EPO levels continued to rise for approximately 1.5 h and after 3 h declined exponentially with an average half-life time of 5.2 h.

Ventilatory, circulatory, endocrine, and renal effects of almitrine infusion in man: a contribution to high altitude physiology

Diuresis at altitude was thought to be the result of chemoreceptor stimulation leading to a reduction of cardiac volume overload. This hypothesis was tested in ten young, healthy subjects by infusion of almitrine (0.5 mg.kg-1 body mass within 30 min) assuming analogous sites of action, i.e. arterial chemoreceptors and pulmonary vessels, for almitrine as for hypoxic hypoxia. The results show that almitrine increases ventilation, heart rate, systolic blood pressure, central venous pressure and natriuresis, but fails to increase significantly atrial natriuretic peptide plasma concentration and diuresis. It is concluded: (1) that almitrine has similar sites of action as hypoxic hypoxia at about 5000 m, (2) that natriuresis during arterial chemoreceptor stimulation might reduce cardiac volume overload, (3) that the volume excretion hypothesis, in particular the pathways from the cardiac volume overload to the water diuresis, need, for an understanding of the hypoxia-induced diuresis, further direct investigations at altitude.

Effects of atropine and propranolol on the respiratory, circulatory, and ECG responses to high altitude in man

In order to analyze the respiratory, cardiovascular, and ECG responses to acute hypoxic hypoxia, three experimental series were carried out in a randomized manner on 11 healthy, unacclimatized volunteers at rest during standardized stepwise exposure to 6000 m (PAO2 35.2 +/- 2.9 mmHg/4.7 +/- 0.4 kPa) in a low-pressure chamber a) without (control), b) with propranolol, and c) with atropine combined with propranolol. The results show that hypoxic hyperventilation and alveolar gases are not affected by activation of the sympatho-adrenal axis or by parasympathetic withdrawal. Sympathetic activity, however, increases heart rate, stroke volume (pulse pressure), estimated cardiac output and systolic blood pressure, whereas decreased parasympathetic activity increases heart rate and estimated cardiac output, but lowers stroke volume. The fall in peripheral resistance, observed during progressive hypoxia in all three groups, is thought to be due to hypoxia-induced depression of the vasomotor center. At altitude catecholamine secretion and vagal withdrawal synergistically account in the ECG for the R-R shortening, the relative Q-T lengthening, the elevation of the P wave and the ST-T flattening. Probable direct hypoxic effects on the heart are the increase in P-Q duration and the minor but still significant depression of the T wave. It is concluded that at altitude increased sympatho-adrenal and decreased parasympathetic activity is without effect on hypoxic hyperventilation, but accounts for most of the cardiovascular and ECG changes. Diminution of sympathetic activity and imminent vagotonia arising after acute ascent to 6000 m probably reflect hypoxia of the central nervous system.

Blockade of pulmonary stretch receptors reinforces diaphragmatic activity during high-frequency oscillatory ventilation

During apneic periods elicited by high-frequency oscillatory ventilation (HFOV) a tonic diaphragmatic activity was observed, contrasting with the absence of diaphragmatic activity during apnea induced by lung inflation. To clarify the mechanism underlying the persistence of the diaphragmatic activity during HFOV-induced arrest of breathing the reflex responses to short periods of HFOV, and to periods of lung inflation with airway pressure (Paw) equal to the mean Paw and/or to maximal Paw during HFOV were examined both before and after the blockade of slowly adapting stretch receptors (SR) by inhalation of sulphur dioxide (SO2) in anaesthetized rabbits. In animals with intact SR, the HFOV-induced reflex apnea lasted longer than that induced by lung inflation, the associated diaphragmatic activity being in the most cases higher than the diaphragmatic activity during quiet expiration; inflation, however, completely inhibited diaphragmatic activity. After blockade of SR, spontaneous breathing continued during periods of lung inflation, i.e., the Hering-Breuer inflation reflex was abolished, whereas HFOV still led to a cessation of spontaneous breathing, the associated diaphragmatic activity even exceeding the level observed during quiet inspiration. From these results we conclude that only one part of the reflex response to HFOV is due to SR-stimulation and that in addition other vagal pulmonary receptors (irritant- and/or C-fibre-receptors) are involved. The stimulation of the latter counterbalances the concomitant stimulation of SR, giving rise to the tonic activity of the diaphragm.

Respiratory phase detection and delay determination for breath-by-breath analysis

The delay between air flow and gas concentration signals is generally assumed to be constant within a breath as well as from breath to breath, but it was not possible to examine the constancy of the delay with the delay determination techniques so far available. Thus we developed new methods for respiratory phase detection and delay determination. The presented algorithm for the detection of the start of inspiration and expiration (phase detection) replaces the generally used valve assembly with two pneumotachographs. Now, the pneumotachograph is used in a bidirectional mode, but with a volume criterion for phase detection replacing the less reliable threshold criterion. To measure the delay between flow and gas concentration signals, a test gas is periodically injected as a marker. This test gas contains less N2 than ambient air. Therefore, the delay is determined as time between the moment of injection and the drop of N2. These two methods rendered it possible to examine delay variations and their consequences. The investigation of various breathing patterns demonstrated that the usually assumed errors caused by delay uncertainty are underestimated. We suggest reliance on a breath-by-breath delay determination to account for delay variations.

A pulsed diagonal-beam ultrasonic airflow meter

The construction and specific function of a new ultrasonic flowmeter are described. The mean velocity of the respiratory airflow is calculated by measuring the transit times of short ultrasonic pulse trains, simultaneously transmitted upstream and downstream at a 500-Hz rate. The flowmeter system consists of a control unit and a separate flow head. The former includes the power supplies, a controlling microprocessor, most of the signal-processing circuitry, and three analog outputs for flow, volume, and temperature. The flow head contains the respiratory tube with a constant circular cross section (length 90 mm, diam 20 mm, dead space 35 ml), a fast temperature sensor, two electronic circuits for processing of flow and temperature data, and a sound transmission channel with two capacitive ultrasonic wide-band transducers. This respiratory airflow meter, suitable for spirometric maneuvers (vital capacity, forced vital capacity) as well as for long-term breath-by-breath respiratory analysis, is extremely fast (response time 1-2 ms) and accurate (volume accuracy with room air +/- 0.7%), with low noise (below 9 ml/s), a wide flow range (bidirectional from 0 to 9 l/s), and a flat frequency response up to 70 Hz.

The effect of propranolol on whole-body microvibrations during examination stress

Whole-body microvibrations (MV) in three dimensions were measured in 51 volunteers, all medical students, 26 without and 25 with beta-receptor blockade (propranolol), immediately before a practical physiology examination and during the ensuing vacation. Propranolol impeded the increase in MV values in all three axes, significantly those in the z axis (vertical), the differences in MV values between the two measurements being minimal in the beta-receptor blocked group. On the other hand, propranolol enhanced MV in the x axis (anteroposterior) and the y axis (transverse), the y axis difference being significant only in females. Propranolol obviously relieves examination stress: the majority of candidates (52%) felt "quieter" in the examination with than in other similar situations without beta-receptor blockade. Propranolol was, however, without effect on the examination results. The rectified impulse in the z axis when related to body weight (Jz) correlates linearly with the calculated cardiac output. Propranolol, however, reduced cardiac output more than Jz, pointing to a Jz component non-sensitive to beta-receptor blockade. The part played by muscle tonus, mainly reflected in the y axis, thus remains unknown. The large and slow oscillations in the x and y axes, observed particularly in beta-receptor blocked females, might be attributed to diminution in standing ability.

Location-dependent characteristics of pulmonary stretch receptor activity in the rabbit

In anaesthetized, thoracotomized and artificially ventilated rabbits, the location of pulmonary stretch receptors (SR) was established by means of local mechanical stimulation as well as by micro-injections of the local anaesthetic cinchocaine. Differences in SR activity were analyzed in relation to the receptor site during specific stimulation by lung inflation, as well as during nonspecific activation by ammonia inhalation. Out of 107 SR, 55% were located in larger airways, i.e., in the trachea, main bronchus and lobar bronchi ("central SR"), whereas 45% were found to lie more peripherally ("peripheral SR"). There were several differences with respect to the discharge pattern evoked by lung inflation and by ammonia inhalation between SR of different locations. The increase of discharge rate evoked by lung inflation and by ammonia inhalation was significantly greater in peripheral than in central SR. Significantly more central than peripheral SR discharged throughout the whole respiratory cycle, i.e., even at end-expiratory lung volume. Furthermore, a delayed inspiratory recruitment as well as a transient cessation of firing after the initial increase of activity, which followed ammonia inhalation, occurred more frequently in central than in peripheral SR.

Effect of coupling the breathing- and cycling rhythms on oxygen uptake during bicycle ergometry

The influence of the degree of coupling between the breathing and cycling rhythms (K) on oxygen uptake (Vo2) was examined in 30 volunteers. They cycled on an ergometer with a load equal to 50% of their work capacity 170 in two experimental runs with spontaneous breathing rhythm, and in a further two runs with acoustically triggered breathing. K was continuously ascertained. Vo2 and other respiratory parameters were measured by an automatic "breath-by-breath analysis" system. In 16 subjects, Vo2-differences between runs were correlated with the differences in K. In the majority of these subjects (12), Vo2 decreased significantly with increasing K. In 14 subjects, Vo2-and K-variations within individual runs were analyzed. Phases with higher K were regularly accompanied by a decrease in Vo2. It is concluded that coupling the breathing and cycling rhythms reduces Vo2 for a given moderate work load, although the magnitude of the Vo2-reduction varies considerably between individuals.

Breathing pattern and stretch receptor activity during high frequency ventilation

In anaesthetized rabbits the effects of high frequency ventilation (HFV) on breathing pattern and on stretch receptor (SR) activity were examined in order to elucidate the mechanism underlying the inhibition of respiration during HFV. An attempt was undertaken to compare the effects of HFV with those of static lung inflations. HFV applied in frequencies between 5 Hz and 25 Hz and with peak airway pressure (Paw) between 5 and 15 cm H2O led - proportionally to Paw - to a gradual prolongation of expiration up to an apnoea. Similar effects occurred during lung inflations, although at higher Paw than during HFV. HFV-induced apnoea was accompanied by a tonic phrenic and diaphragmatic activity which was absent during inflation-induced apnoea. In addition to the activity due to spontaneous breathing, during HFV the SR discharge rate increased with each positive airflow pulse particularly in the expiratory phase, whereas the inspiratory discharge rate was less affected. During static lung inflations there was a parallel increase of both inspiratory and expiratory SR activity, the expiratory discharge rate, however, remaining lower and the inspiratory discharge rate rising more than during HFV. It is concluded that the HFV-induced increase of expiratory SR discharge rate may account for the inhibition of spontaneous breathing during HFV. The persistence of phrenic and diaphragmatic activity during HFV-induced apnoea is thought to be due to activation of irritant receptors.

The ECG changes due to altitude and to catecholamines

In order to distinguish the effects of beta-receptor stimulation on the ECG from other factors during short-term adjustment to hypoxic aerohypoxia, the ECG of 19 volunteers were compared during moderately acute, stepwise exposure to high altitude (6,000 m) in a low pressure chamber, once with and once without beta-receptor blockade (propranolol), and after isoprenaline inhalation at ground level. The results show that beta-receptor stimulation accounts mainly for most ECG changes during altitude exposure, i.e., for the shortening of R-R interval, the lengthening of Q-T and in particular for the ST-T flattening, the latter therefore being only an indirect sign of hypoxia. After exclusion of the catecholamines, the minor but still significant ECG changes at altitude (shortening of R-R interval, increase of P wave, prolongation of P-Q, deviation of the R vector, T wave flattening in the left precordial leads) may be attributed to other, so far undefined factors, such as cardiac hypoxia, vagal withdrawal, or increase of pulmonary resistance.

[Effect of catecholamines and propranolol on the acute acclimatization to high altitude in man]

The venous concentrations of epinephrine and norepinephrine and changes in ventilation, respiratory gases, circulation and ECG were determined in 20 young healthy male medical students during standardized stepwise ascent to 6000 m in a low pressure chamber, once without (control) and once with beta-receptor blockade (propranolol). The results show that the plasma concentration of norepinephrine increased significantly as a result of hypoxic hypoxia. The moderate increase in epinephrine was, besides the minor but significant hypoxic influence, mainly due to psychic tension. Since beta-receptor blockade does not prevent the respiratory and circulatory adjustment, beta-adrenergic stimulation is not thought to be necessary at altitude. Propranolol, on the contrary, lowers the hypoxia-induced increase in cardiac output and diminishes the ECG changes, in particular the S-T depression, significantly. By antagonizing the effects of epinephrine and by its central effects, propranolol improves subjective tolerance to altitude, and, on the other hand, by economizing the cardiac work load, the objective ability to withstand oxygen want.

The effect of pulmonary stretch receptor activity on the respiratory response to ammonia-inhalation

The contribution of pulmonary stretch receptor (SR) activity to the changes in breathing pattern (f, VT, tI, tE, tI: tE) following inhalation of ammonia vapour has been studied in rabbits at three levels of lung distension, i.e., three levels of SR activity, and during reversible SO2-blockade of SR. The result show that the increase in breathing frequency (f) and the decrease in tidal volume (VT) due to ammonia inhalation are almost identical for animals with and without blockade of SR, whereas the duration of inspiration and expiration (tI, tE) as well as their relationship (tI:tE) vary considerably, the variations depending on the level of SR activity. For a given tI the expiration was longer in animals with SR intact than in animals with SR blocked. It is concluded that in rabbits the increased activity of SR after inhalation of ammonia counteracts significantly the predominant effects of irritant (deflation) receptor stimulation, thus rendering possible a longer expiration.

Relation between pedalling- and breathing rhythm

The relationship between pedalling- and breathing rhythm was studied in 34 medical students (non-cyclists") and 10 racing cyclists on an electromagnetic bicycle-ergometer, the effective work load of which (50 W, 100 W, 150 W, 200 W) was independent of the pedalling rate. The criteria used were integer p/b ratios (pedalling rate being a multiple of breathing frequency) and phase coupling (the breathing phases starting preferentially at a certain angle of the pedalling cycle). Unconsciously occurring coordination of pedalling and breathing rhythm was found in the majority of the test persons; 70%-100% of the racing cyclists, 50%-63% of the regularly breathing and 25%-33% of the decreased with increasing work load. Phase coupling was even more frequent than integer p/b ratios and was not affected by increasing work load. The majority of racing cyclists (unlike the non-cyclists) coupled the inspiration-onset with the onset of either the left or the right leg movement. Expiratory phase coupling, however, was analogous in all groups; expiration began preferentially at mid-contraction of either leg. The results are discussed in terms of relative (nervous) coordination. It is concluded that the tendency to coordination between pedalling- and breathing rhythm increases with pedalling training and with regularity of breathing.

Propranolol and the respiratory, circulatory, and ECG responses to high altitude

The role of the sympatho-adrenal system in the acute respiratory and cardiovascular responses to high altitude was studies in 20 volunteers during ascent to 6,000 m in a low pressure chamber, once without (control) and once with beta-adrenergic blockade. Special attention was paid to the hypoxia-induced ECG changes. Propranolol lowered the level of hypoxia-induced cardiovascular reactions, whereas it had no effect on hypoxic hyperventilation and alveolar gases. At altitude, ECG changes during myocardial depolarization occurred in both the propranolol and the control groups, probably due to the direct effects of hypoxia. During the repolarization phase, propranolol led to an almost complete abolition of S-T depression and to significant reduction of T wave flattening. The minor but still significant flattening of the T wave as well as the relative (to the heart rate) lengthening of Q-T is probably due to the direct effects of hypoxia. Propranolol abolishes or diminishes the signs of cardiac hypoxia by antagonizing the effects of catecholamine release and/or by reducing myocardial oxygen consumption, thus probable increasing the ability to withstand oxygen-want at altitude.

Comparison of hypoxanthine, lactate, and ECG signs as indicators of hypoxia

High altitude-induced hypoxemia in 26 young adults was used to compared hypoxia parameters such as blood lactate, hypoxia-induced electrocardiogram signs, and the recently proposed plasma hypoxanthine concentration. At a PaO2 of 30 mm Hg, no elevation in hypoxanthine and small increase in lactate was observed. Minimal leg exercise was added to further increase hypoxic during hypoxemia. A significant increase in lactate and considerable ST-T depression in electrocardiogram indicated hypoxia, but no change in plasma hypoxanthine was found. Work-dependent hyperventilation as a main cause of lactate elevation was excluded. Blockade of hypoxanthine breakdown by allopurinol in vivo increased plasma hypoxanthine levels, but hypoxemia with or without leg exercise failed to consistently increase this level further. Elevations of blood lactate above the normal range were found at a PaO2 of 30 mm Hg and below.