The quest for an animal model of high altitude pulmonary edema

The understanding of the mechanisms underlying certain human diseases usually requires an animal model which can be manipulated in a way that will allow dissection of the pathophysiologic events which lead to the disease. High altitude pulmonary edema (HAPE) occurs in some healthy individuals who ascend from low to high altitude. The disease is characterized by a high protein leak into the lungs and is associated with accentuated pulmonary hypertension. Attempts to find an animal model for HAPE have been made in a number of animal species, including rats, rabbits, sheep, dogs and ferrets. None has been consistently successful. Utilizing the physiologic characteristic of an accentuated hypoxic pulmonary vascular response, we studied both pigs and rats during the stresses of hypoxia and exercise (rats) and examined the lungs for the cellular, protein, and morphologic changes. Protein and cell contents in the lung lavage of the hypoxic animals were slightly higher than the controls while the presence of von Willebrand factor in the hypoxic animals suggests early epithelial damage. This presentation will review previous attempts to find an animal model of HAPE and will discuss the preliminary results of our studies with their suggestive but not confirmatory results.

Effect of age on bronchodilator response

STUDY OBJECTIVE

Our objective was to compare the differential effects of age and drug type on bronchodilator response.

DESIGN

The design was an unblinded, randomized crossover study.

SETTING

An ambulatory pulmonary drug study unit was the setting.

PATIENTS

Nineteen young (18 to 25 yr) and 17 elderly (greater than 65 yr) stable asthmatic subjects were studied.

INTERVENTIONS AND MEASUREMENTS

Albuterol or ipratropium was given on two separate mornings using an MDI with extender. Subjects inhaled two puffs initially and then one puff every 30 min to a total of six puffs. Pulmonary function, blood pressure, and pulse were measured at baseline and every 30 min for 3 h.

RESULTS

All subjects had a greater than 15 percent increase in FEV1 with one or both drugs. More patients responded to albuterol than to ipratropium in both age groups. The maximum percentage of change from baseline was greater (p less than 0.05) with albuterol (mean, 40.1 percent in young and 60.5 percent in old) than with ipratropium (21.2 percent in young; 31.2 percent in old) in both groups. These differences remain significant after correction for baseline differences using area-under-the-curve analysis of the percent of maximum improvement; however, the differences between age groups for the same drug were not statistically significant by either index of change. There were also no differences between drugs or between age groups for time (or number of puffs) to reach maximum improvement (mean, 2.0 to 2.2 h for albuterol and 1.6 to 1.7 h for ipratropium). The changes in FVC and FEF25-75% were similar to FEV1. Changes in blood pressure and pulse were not significant. Three subjects stopped therapy with albuterol with side effects.

CONCLUSIONS

Both drugs are effective bronchodilators in young and old asthmatic subjects, but albuterol results in a greater magnitude of response in both age groups. Age is not a predictor of response to either drug.

Brain tissue pH and ventilatory acclimatization to high altitude

31P nuclear magnetic resonance spectroscopy (31P-NMRS) was performed on brain cross sections of four human subjects before and after 7 days in a hypobaric chamber at 447 Torr to test the hypothesis that brain intracellular acidosis develops during acclimatization to high altitude and accounts for the progressively increasing ventilation that develops (ventilatory acclimatization). Arterial blood gas measurements confirmed increased ventilation. At the end of 1 wk of hypobaria, brain intracellular pH was 7.023 +/- 0.046 (SD), unchanged from preexposure pH of 6.998 +/- 0.029. After return to sea level, however, it decreased to 6.918 +/- 0.032 at 15 min (P less than 0.01) and 6.920 +/- 0.046 at 12 h (P less than 0.01). The ventilatory response to hypoxia increased [from 0.35 +/- 0.11 (l/min)/(-%O2 saturation) before exposure to 0.69 +/- 0.19 after, P = 0.06]. Brain intracellular acidosis is probably not a supplemental stimulus to ventilatory acclimatization to high altitude. However, brain intracellular acidosis develops on return to normoxia from chronic hypoxia, suggesting that brain pH may follow changes in blood and cerebrospinal fluid pH as they are altered by changes in ventilation.

Renal carbonic anhydrase inhibition reduces high altitude sleep periodic breathing

The efficacy of carbonic anhydrase (CA) inhibitors in amelioration of periodic breathing during sleep at high altitude is not fully understood. Although CA is present in a number of tissues, we hypothesized that selective renal CA inhibition without physiologically important inhibition of other tissue CA, may be sufficient alone by its generation of a mild metabolic acidosis to stimulate ventilation and prevent periodic breathing. We studied benzolamide (3 mg/kg), a selective inhibitor of renal CA, in 4 climbers on ventilation and ventilatory responses at sea level and on arterial O2 saturation (SaO2%) and periodic breathing during sleep at altitude. At sea level, ventilation increased and PaO2 rose accompanied by a mild metabolic acidosis. The isocapnic hypoxic ventilatory response was unchanged but the hyperoxic hypercapnic ventilatory response rose 40%. At high altitude (4400 m), daytime SaO2% improved from 81 to 85 and venous plasma HCO3- fell from 18.9 to 14.8 mM. During sleep, mean SaO2% rose from 76 to 80 and periodic breathing decreased 75%. We conclude that metabolic acidosis occurring with all CA inhibitors is one of the major stimulant actions of these drugs on ventilation while awake and during sleep at high altitude.

Exercise breathing pattern during chronic altitude exposure

Breathing pattern in response to maximal exercise was examined in four subjects during a 7-day acclimatisation to a simulated altitude of 4247 m (barometric pressure, PB = 59.5 kPa). Graded exercise tests to exhaustion were performed during normoxia (day 0), and on days 2 and 7 of hypoxia, respectively. Ventilation was significantly augmented in the hypoxic environment, as were both the mean inspiratory flow (VT/TI) and inspiratory duty cycle (TI/TTOT) components of it. VI/TI was increased due to a significant increase in tidal volume (VT) and a corresponding decrease in inspiratory time duration (TI). Throughout a range of exercise ventilation, TI/TTOT was increased due to an apparently greater decrease in expiratory time duration (TE) with respect to TI. In all cases, the relation between VT and TI displayed a typical range 2 behaviour, with evidence of a range 3 occurring at very high ventilatory rates. There was essentially no difference observed in the VT-TI relation during exercise between the normoxic and hypoxic conditions. No significant changes were observed in the breathing pattern in response to exercise within the exposure period (from day 2 to day 7), although there was a discernible tendency to a higher stage 3 plateau by day 7 of altitude exposure.

Operation Everest II: ventilatory adaptation during gradual decompression to extreme altitude

To assess the ventilatory adaptation during gradual ascent to extreme altitude, we studied seven healthy males as part of the 40 d simulated ascent of Mt. Everest in a hypobaric chamber. We measured resting ventilation (VE, l.min-1), arterial oxygen saturation (SaO2%), the ventilatory response to oxygen breathing, isocapnic hypoxic ventilatory response (HVR), and hypercapnic ventilatory response (HCVR) at sea level prior to the ascent (760 torr), 14,000 feet (428 torr), 24,000 feet (305 torr), and within 24 h of descent (765 torr). VE increased from 9.3 +/- 1.1 l.min-1 at 760 torr to 23.4 +/- 1.3 l.min-1 at 305 torr and remained elevated at 14.7 +/- 0.7 l.min-1 after descent. Oxygen breathing decreased VE by 9.6 +/- 1.3 l.min-1 at 305 torr. Isocapnic HVR (expressed as a positive slope of VE/SaO2, l.min-1.%SaO2(-1) increased from 0.18 +/- 0.07 at 760 torr to 0.34 +/- 0.11 and 0.38 +/- 0.5 at 428 torr and 305 torr (P less than 0.05) respectively. HVR was elevated further upon return to sea level (0.8 +/- 0.09, P less than 0.05). HCVR (S = VE/PETCO2, l.min-1.torr-1) increased from sea level (S = 4.4 +/- 0.09) to 305 torr (S = 18.7 +/- 3.5, P less than 0.01) and remained elevated upon return to sea level (S = 10.7 +/- 4.6, P less than 0.001). This study is the first to investigate the ventilatory response to such extreme altitude and so soon after descent and shows that hypoxic and hypercapnic responses increase during prolonged progressive hypoxic exposure and remain significantly elevated from pre-ascent levels immediately upon descent.

Steady-state infusions of opioids in human. II. Concentration-effect relationships and therapeutic margins

We used computer-controlled individually tailored infusions to study relationships between plasma drug concentration and opioid effects, and to evaluate the therapeutic margins of alfentanil, fentanyl and morphine in human subjects. In order to compare the 3 drugs, we infused each opioid to 3 different steady-state target plasma concentrations during separate 8 h test periods so that concentration-effect curves could be defined for each opioid and subject. Dental electrical stimulation produced a consistent degree of baseline experimental pain, and we measured the influence of increasing plasma opioid concentrations on pain intensity and the magnitude of pain-related evoked potentials. We also quantified ventilatory function and subjective side-effects during baseline (no drug), at the 3 target plasma concentrations with each drug. Finally, we measured actual plasma opioid concentrations during each phase of the infusion period. This procedure allowed us to calculate for each opioid the plasma concentration required to produce a 50% decrease in reported pain intensity and evoked potential amplitude (IC50). Subsequent calculation of side-effect magnitudes at the analgesic IC50s permitted direct comparisons of therapeutic margins between alfentanil, fentanyl and morphine. We found a robust relationship between plasma drug concentration and analgesic, ventilatory, and subjective-effect magnitudes for each opioid in this study. We conclude that the magnitudes of individual side-effects associated with equianalgesic, steady-state plasma concentrations of these 3 mu receptor-selective opioids do not differ across drugs.

The cost to the central nervous system of climbing to extremely high altitude

To assess the possibility that climbing to extremely high altitude may result in hypoxic injury to the brain, we performed neuropsychological and physiologic testing on 35 mountaineers before and 1 to 30 days after ascent to altitudes between 5488 and 8848 m, and on 6 subjects before and after simulation in an altitude chamber of a 40-day ascent to 8848 m. Neuropsychological testing revealed a decline in visual long-term memory after ascent as compared with before; of 14 visual items of information on the Wechsler Memory Scale, fewer were recalled after ascent by both the simulated-ascent group (a mean [+/- SD] of 10.14 +/- 1.68 items before, as compared with 7.00 +/- 3.35 items after; P less than 0.05) and the mountaineers (12.33 +/- 1.96 as compared with 11.36 +/- 1.88; P less than 0.05). Verbal long-term memory was also affected, but only in the simulated-ascent group; of a total of 10 words, an average of 8.14 +/- 1.86 were recalled before simulated ascent, but only 6.83 +/- 1.47 afterward (P less than 0.05). On the aphasia screening test, on which normal persons make an average of less than one error in verbal expression, the mountaineers made twice as many aphasic errors after ascent (1.03 +/- 1.10) as before (0.52 +/- 0.80; P less than 0.05). A higher ventilatory response to hypoxia correlated with a reduction in verbal learning (r = -0.88, P less than 0.05) and with poor long-term verbal memory (r = -0.99, P less than 0.01) after ascent. An increase in the number of aphasic errors on the aphasia screening test also correlated with a higher ventilatory response to hypoxia in both the simulated-ascent group (r = 0.94, P less than 0.01) and a subgroup of 11 mountaineers (r = 0.59, P less than 0.05). We conclude that persons with a more vigorous ventilatory response to hypoxia have more residual neurobehavioral impairment after returning to lower elevations. This finding may be explained by poorer oxygenation of the brain despite greater ventilation, perhaps because of a decrease in cerebral blood flow caused by hypocapnia that more than offsets the increase in arterial oxygen saturation.

Respiratory adaptation in the highest inhabitants and highest Sherpa mountaineers

Arterial blood gases, acid-base and hematocrit of six highest inhabitants on Aucanquilcha (5950 m) in Chile were studied. These blood gases were compared with the alveolar gases of highest mountain climbers in Nepal, Sherpas and acclimatized lowlanders, and on average high altitude natives in the Chilean and Peruvian Andes and in the Nepal Himalayas. The mean arterial PCO2 (27.5 Torr) was lower than the standard sea level normal values, indicating a modest hypoxic hyperventilation. The mean arterial pH was 7.400, showing a complete renal compensation of respiratory alkalosis. The mean hematocrit (62%) and hemoglobin (20.7 g/dl) values were greater than the standard sea level values. These blood data showed that the highest inhabitants were acclimatized to hypoxia of their residential altitude. The respiratory gases showed less hyperventilation in the highest inhabitants and Sherpa mountaineers of high altitudes relative to the acclimatized lowlanders. Also, the average high altitude natives in the Andes and Himalayas showed less hyperventilation compared to the acclimatized lowlanders. We conclude that the attenuated hyperventilation is an appropriate respiratory adaptation to high altitude hypoxia in the native high altitude residents, allowing them to conserve metabolic energy expended for hyperventilation and to use the ventilatory reserve for a better performance at greater altitudes.

Ventilatory response to rowing and cycling in elite oarswomen

Rowing is a unique exercise for humans, and the imposed biomechanical motion may alter both respiratory mechanics and timing. To investigate the ventilatory patterns of competitive rowers while rowing, we studied the pulmonary function of eight members of the University of Washington Women's Crew and one former member of the 1984 Women's Olympic Rowing Team on a rowing ergometer. Ventilatory performance of the oarswomen was compared both with their performance to exhaustion on a cycle ergometer and with the ventilatory response of six untrained controls on a rowing and a cycle ergometer. We found rowing elicited a higher ventilatory response in both the oarswomen and controls in submaximal and maximal work loads (P less than 0.001). Both oarswomen and controls had higher maximal breathing frequencies when rowing compared with cycling [rowers, 54.7 +/- 1.9 vs 49.8 +/- 0.09 (SE) breaths/min, P less than 0.05; and controls, 53.6 +/- 2.5 vs. 49.2 +/- 4.7, P less than 0.05] and lower maximal tidal volumes (rowers, 1.94 +/- 0.12 vs. 2.21 +/- 0.09 liters, P less than 0.01; controls, 1.59 +/- 0.09 vs. 1.68 +/- 0.19, difference not significant). Both oarswomen and controls were more hypocapnic while rowing compared with cycling (rowers, P less than 0.001; controls, P less than 0.02), although oarswomen were less hypocapnic while rowing than nonrowers (P less than 0.03). These results indicate that rowing causes hyperventilation with a higher breathing frequency and lower tidal volume. This alteration of pattern is possibly secondary to a change in mechanics, which possibly arises from the generation of high exercise ventilation in a variable seated position.

Predicting maximum oxygen uptake in adolescents

The purpose of this study was to develop regression equations to predict oxygen uptake (VO2) in adolescents. Thirty-nine subjects had maximum oxygen uptake measured on a cycle ergometer. Anthropometric measurements included triceps, subscapular, and thigh skin folds. The subjects ran 12-minute and 2.4-km runs on separate days. Using a multiple-stepwise forward regression analysis, equations were developed to predict oxygen uptake as VO2 and VO2/kg, accounting for 81% and 64% of the variance, respectively. A validation procedure was done 5 months later when all runs and measurements were repeated, and predicted and measured oxygen uptake were compared. The equation for predicting VO2 accounted for 88% of the variance, with the SE of the estimate equal to 0.07 L/min. The equation for predicting VO2/kg accounted for 58% of the variance, with the SE of the estimate equal to 27 mL of oxygen per kilogram of body weight per minute. The VO2 can be accurately predicted using indirect means in adolescents, while VO2/kg cannot.

Recovery of airway protection compared with ventilation in humans after paralysis with curare

d-Tubocurarine (dTc) was administered intravenously to six healthy unanesthetized volunteers to assess the sensitivity to neuromuscular blockade of those muscles involved in protecting the airway against obstruction and/or aspiration relative to the muscles of inspiration. Each subject was given an intravenous bolus of dTc followed by an infusion to allow three different levels of inspiratory muscle weakness as measured by maximum inspiratory pressure (MIP). Levels of MIP were control (-90 cm H2O), -60, -40, and -20 cm H2O. Vital capacity (VC), hand grip strength (HGS), and end-tidal CO2 (PETCO2) were obtained at each level. At each level of weakness and at intermediate values during recovery, muscles of airway protection were functionally assessed by noting the MIP at which the maneuver could be accomplished and the MIP at which they could not. The mean of these two values was calculated for each subject. The tests were: 1) ability to swallow, 2) ability to perform a valsalva maneuver, 3) prevent obstruction of the airway, and 4) ability to approximate teeth. These were compared with head lift and straight leg raising. At maximum neuromuscular blockade (MIP of -20 cm H2O), VC was 2.0 liters, HGs was 0, and PETCO2 was normal. Muscles of airway protection were still incapacitated. Swallowing returned above MIP of -43 cm H2O, approximation of teeth above -42 cm H2O, airway obstruction above -39 cm H2O, and valsalva above -33 cm H2O. Thus, although ventilation may be adequate at MIP = -25 mmHg, the muscles of airway protection are still nonfunctional.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intercostal nerve blockade on respiratory mechanics and CO2 chemosensitivity at rest and exercise

Lower intercostal and abdominal muscles interact with other respiratory muscles to produce inspiration as well as expiration. Intercostal nerve blockade from T6-T12 was produced in seven healthy males to study its effect on: 1) supine pulmonary function, 2) inspiratory effort, 3) hypercapnic ventilatory response, including mouth occlusion pressures with and without an expiratory load, and 4) ventilation during progressive exercise on a cycle ergometer. Studies during control and blocked states were performed on different days. Lower chest and abdominal wall paralysis was documented with electromyography. Findings include a minimal decrease in peak expiratory flows with intercostal blockade (P = 0.02), but no other changes in supine resting pulmonary function tests, inspiratory effort, or hypercapnic ventilatory response slopes. Minute ventilation, respiratory rate, and VT/TI during exercise were also minimally increased, indicating an increase in the drive to breathe, which was unrelated to a change in metabolic rate. During exercise, total time to exhaustion was decreased following intercostal nerve blockade. Bilateral intercostal nerve blockade produced minimal decreases in peak expiratory flow at rest in supine subjects. During seated exercise, there was a slight increase in respiratory drive, probably due to minor alterations in the mechanics of breathing induced by intercostal blockade. The authors conclude that, in healthy young subjects, intercostal nerve blockade does not exert a clinically significant adverse affect on pulmonary mechanics and that ventilatory function is well-maintained even at extremes of ventilatory demand.

Increased muscle efficiency and sustained benefits in an outpatient community hospital-based pulmonary rehabilitation program

Previous reports of pulmonary rehabilitation programs have demonstrated improvement in exercise capacity in subjects with disabling pulmonary disease. However, the cost-effectiveness, benefits to outpatients in a community setting, durability of these improvements, and mechanism of improved exercise capacity remain unclear. Forty-four patients with an average FEV1 of 33 +/- 4 percent of predicted completed a six-week long period of supervised treadmill exercise, as well as a continuing home program. Twenty percent had previously unsuspected cardiac disease discovered through the program, while 36 percent had previously unsuspected exercise desaturation. Cardiopulmonary stress testing before and after the program revealed a 73 +/- 16 percent improvement in aerobic capacity (METs peak [power]) and a 250 +/- 78 percent improvement in endurance (MET-min [work]). No significant change was seen in VE max, HR max, FEV1, or the degree of exercise desaturation. Only a small improvement was noted in VO2 max (15 +/- 8 percent) and O2 pulse (16 +/- 8 percent), suggesting that most of the improvement was due to improved muscle efficiency. Follow-up testing at 12 +/- 3 months in 24 subjects revealed that 89 +/- 7 percent of the peak exercise performance was maintained. The cost of the basic program was +800. The results demonstrated that an outpatient community hospital pulmonary rehabilitation program can accomplish substantial exercise capacity improvement with sustained benefits in a cost-effective manner.

High-Altitude Pulmonary Edema: The Disguised Killer

In brief: High-altitude pulmonary edema afflicts 1% to 2% of sojourners above 10,000 to 11,000 ft. It is at the severe end of a spectrum of high-altitude illnesses; symptoms can be subtle or overt and can rapidly progress to coma and death. The best prevention is acclimatization-slow, gradual ascent that allows the body to adapt to a hypoxic environment. The author reviews the signs and symptoms and how to recognize them, the pathophysiology, and the prevention and management of this avoidable, but potentially fatal, condition.

The lung at high altitude: bronchoalveolar lavage in acute mountain sickness and pulmonary edema

High-altitude pulmonary edema (HAPE), a severe form of altitude illness that can occur in young healthy individuals, is a noncardiogenic form of edema that is associated with high concentrations of proteins and cells in bronchoalveolar lavage (BAL) fluid (Schoene et al., J. Am. Med. Assoc. 256: 63-69, 1986). We hypothesized that acute mountain sickness (AMS) in which gas exchange is impaired to a milder degree is a precursor to HAPE. We therefore performed BAL with 0.89% NaCl by fiberoptic bronchoscopy in eight subjects at 4,400 m (barometric pressure = 440 Torr) on Mt. McKinley to evaluate the cellular and biochemical responses of the lung at high altitude. The subjects included one healthy control (arterial O2 saturation = 83%), three climbers with HAPE (mean arterial O2 saturation = 55.0 +/- 5.0%), and four with AMS (arterial O2 saturation = 70.0 +/- 2.4%). Cell counts and differentials were done immediately on the BAL fluid, and the remainder was frozen for protein and biochemical analysis to be performed later. The results of this and of the earlier study mentioned above showed that the total leukocyte count (X10(5)/ml) in BAL fluid was 3.5 +/- 2.0 for HAPE, 0.9 +/- 4.0 for AMS, and 0.7 +/- 0.6 for controls, with predominantly alveolar macrophages in HAPE. The total protein concentration (mg/dl) was 616.0 +/- 3.3 for HAPE, 10.4 +/- 8.3 for AMS, and 12.0 +/- 3.4 for controls, with both large- (immunoglobulin M) and small- (albumin) molecular-weight proteins present in HAPE.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal control of ventilation in high-altitude pulmonary edema

We wished to determine the role of hypoxic chemosensitivity in high-altitude pulmonary edema (HAPE) by studying persons when ill and upon recovery. We studied seven males with HAPE and seventeen controls at 4,400 m on Mt. McKinley. We measured ventilatory responses to both O2 breathing and progressive poikilocapnic hypoxia. Hypoxic ventilatory response (HVR) was described by the slope relating minute ventilation to percent arterial O2 saturation (delta VE/delta SaO2%). HAPE subjects were quite hypoxemic (SaO2% 59 +/- 6 vs. 85 +/- 1, P less than 0.01) and showed a high-frequency, low-tidal-volume pattern of breathing. O2 decreased ventilation in controls (-20%, P less than 0.01) but not in HAPE subjects. The HAPE group had low HVR values (0.15 +/- 0.07 vs. 0.54 +/- 0.08, P less than 0.01), although six controls had values in the same range. The three HAPE subjects with the lowest HVR values were the most hypoxemic and had a paradoxical increase in ventilation when breathing O2. We conclude that a low HVR plays a permissive rather than causative role in the pathogenesis of HAPE and that the combination of extreme hypoxemia and low HVR may result in hypoxic depression of ventilation.

High-altitude pulmonary edema: pathophysiology and clinical review

High-altitude pulmonary edema (HAPE) affects young, healthy climbers in an unpredictable fashion. It is potentially fatal, and its underlying pathophysiology is not thoroughly understood. The history and clinical presentation of HAPE, as well as the known underlying pathophysiology, are reviewed. For instance, in HAPE there is an association with blunted respiratory drives to hypoxia and accentuated hypoxic pulmonary vasoconstriction. Recent data show that HAPE is a high permeability leak of protein into the alveolar space associated with an influx of alveolar macrophages. These data have been obtained recently by fiberoptic bronchoscopy in the field setting of Mt McKinley at 4,400 m. The approach to recognition and treatment that involves primarily descent and/or oxygen is discussed.

Control of ventilation in elite synchronized swimmers

Synchronized swimmers perform strenuous underwater exercise during prolonged breath holds. To investigate the role of the control of ventilation and lung volumes in these athletes, we studied the 10 members of the National Synchronized Swim Team including an olympic gold medalist and 10 age-matched controls. We evaluated static pulmonary function, hypoxic and hypercapnic ventilatory drives, and normoxic and hyperoxic breath holding. Synchronized swimmers had an increased total lung capacity and vital capacity compared with controls (P less than 0.005). The hypoxic ventilatory response (expressed as the hyperbolic shape parameter A) was lower in the synchronized swimmers than controls with a mean value of 29.2 +/- 2.6 (SE) and 65.6 +/- 7.1, respectively (P less than 0.001). The hypercapnic ventilatory response [expressed as S, minute ventilation (1/min)/alveolar CO2 partial pressure (Torr)] was no different between synchronized swimmers and controls. Breath-hold duration during normoxia was greater in the synchronized swimmers, with a mean value of 108.6 +/- 4.8 (SE) vs. 68.03 +/- 8.1 s in the controls (P less than 0.001). No difference was seen in hyperoxic breath-hold times between groups. During breath holding synchronized swimmers demonstrated marked apneic bradycardia expressed as either absolute or heart rate change from basal heart rate as opposed to the controls, in whom heart rate increased during breath holds. Therefore the results show that elite synchronized swimmers have increased lung volumes, blunted hypoxic ventilatory responses, and a marked apneic bradycardia that may provide physiological characteristics that offer a competitive advantage for championship performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Butorphanol improves CO2 response and ventilation after fentanyl anesthesia

We have determined that the mixed agonist-antagonist narcotic, butorphanol, improves CO2 response and ventilation after fentanyl anesthesia. A tentative dosage range has been established. Twenty-two patients were anesthetized with isoflurane, nitrous oxide, and fentanyl, which was continuously infused throughout the study. Postoperatively three 1-mg doses of butorphanol were administered IV. Blood pressure, heart rate, plasma epinephrine and norepinephrine concentrations, and pain intensity were essentially unchanged after butorphanol. Most of the improvement in breathing occurred after the first 1-mg dose. Mean respiratory rate increased from 7.8 +/- 5.0 to 11.0 +/- 4.8 min-1 (P less than or equal to 0.005), tidal volume increased from 469 +/- 302 to 844 +/- 390 ml (P less than or equal to 0.005), minute ventilation increased from 4.32 +/- 2.97 to 8.51 +/- 3.14 L/min (P less than or equal to 0.005), and the slope of the ventilatory response to CO2 increased from 0.36 +/- 0.37 to 0.90 +/- 0.80 L X min-1 X mm Hg-1 (P less than or equal to 0.05). Resting PaCO2 decreased from a baseline of 57.8 +/- 11.1 to 51.7 +/- 5.12 mm Hg (P less than or equal to 0.05) after the third dose.

Prediction of successful ventilator weaning using airway occlusion pressure and hypercapnic challenge

We studied eleven patients during 14 attempts at weaning from mechanical ventilation to determine whether central ventilatory drive, measured as airway occlusion pressure 0.1 s after onset of inspiration (P 0.1), during spontaneous breathing before and during a brief hypercapnic challenge, could accurately predict the success or failure of the attempt. All patients were recovering from acute respiratory failure and could breathe spontaneously for 20 minutes on a T-piece but were judged clinically to be marginal weaning candidates. Minute ventilation (VI) and P 0.1 were measured while breathing spontaneously and were repeated during a hypercapnic challenge that raised end-tidal PCO2 approximately 10 mm Hg. Seven of the 14 weaning attempts were unsuccessful, requiring reinstitution of mechanical ventilation. Although the failure group had lower mean maximum inspiratory force and higher spontaneous respiratory rate, no threshold value separated the failure from the success group. Ventilation increased more during hypercapnic challenge in those patients whose weaning attempt was successful, but overlap of results between the two groups rendered this test inaccurate for predicting weaning success. In contrast, successfully weaned patients had greater augmentation of P 0.1 during hypercapnia, expressed as the ratio of P 0.1 during CO2-stimulated to P 0.1 during baseline values, than did those who failed weaning (p less than 0.005). This ratio succeeded, and was thus both specific and sensitive as a predictor of successful weaning from mechanical ventilation in these patients.

Respiratory stimulants and sleep periodic breathing at high altitude. Almitrine versus acetazolamide

We studied the effects of almitrine, acetazolamide, and placebo on the hypoxic ventilatory response (HVR), sleep periodic breathing, and arterial oxygen saturation (SaO2) in 4 healthy climbers. In a laboratory on Denali (Mt. McKinley) at 4,400 m (PB = 440 mm Hg), we used a double-blind, randomized, three-way crossover design. The HVR was measured during the waking state. Periodic breathing and SAO2% were measured during 3-h sleep studies. Almitrine and acetazolamide both increased SaO2% during sleep, although almitrine increased periodic breathing, whereas acetazolamide decreased periodic breathing. The HVR (delta VE/delta SaO2%) was doubled with almitrine (p less than 0.05), but unchanged with acetazolamide. The HVR was positively related to periodic breathing (p less than 0.05). We conclude that periodic breathing during sleep at high altitude is related to the hypoxic ventilatory response, and that acetazolamide is a superior agent to almitrine for ameliorating periodic breathing.

Evaluation of breathlessness in asbestos workers. Results of exercise testing

We studied 120 asbestos-exposed workers seeking compensation for asbestos-related ventilatory impairment who were referred to us for evaluation of their complaint of dyspnea. We reviewed history, chest radiographs, pulmonary function studies, and exercise tests. The workers were 59.9 +/- 9.5 (mean +/- SD) yr of age and their first asbestos exposure had been 34.4 +/- 10 yr prior to the study; 63% were smokers, 19% were ex-smokers, and 18% were nonsmokers. Chest radiographs were normal in 4%, showed only pleural disease in 35%, only parenchymal diseases in 5%, and pleuroparenchymal disease in 56%. Restrictive pulmonary function abnormalities were present in 25% of the workers, and obstructive abnormalities were present in 27%. Because the impairment of one of several organ systems (i.e., ventilatory, cardiac, pulmonary vascular, or peripheral circulatory) may limit exercise performance, we designed an exercise test score in an attempt to identify the system causing the limitation. No abnormal limitation was detectable in half (49.2%) of the subjects. Only 26% had a ventilatory limitation, which was much more frequent in smokers (32%) than in nonsmokers (9%) (p less than 0.05). Unexpectedly, rather more (37%) had a cardiac rather than a ventilatory limitation. We conclude that the complaint of dyspnea in these asbestos-exposed workers was usually not caused by a ventilatory dysfunction.