Left Ventricular Diastolic Function in a Population Sample of Elderly Men

BACKGROUND AND METHODS: Echocardiography with Doppler has been widely used to assess left ventricular (LV) diastolic function. Interpretation of the diastolic indices that are derived, however, is confounded by the effects of physiological aging on the LV diastolic function. In this study, the usefulness of different Doppler-derived indices of LV diastolic function was assessed in elderly subjects by using data from a health screening survey of 584 men aged 70 years. RESULTS: The index of early versus late transmitral blood flow, the E/A ratio, was found to be reduced in the apparently healthy subgroup (n = 195) of the population (0.96 +/- 0.25) compared with previous data from middle-aged subjects. However, E/A ratios similar to those in the apparently healthy subjects were found in subjects with coronary heart disease (CHD), hypertension, and diabetes mellitus. Only subjects with systolic dysfunction (ejection fraction < 40%) showed a significantly decreased E/A ratio (0.79 +/- 0.21, P < 0.05) compared with the apparently healthy subjects. Isovolumic relaxation time (IVRT) was, however, significantly prolonged in subjects with CHD or hypertension compared with the apparently healthy subjects (139 +/- 32, 127 +/- 25, and 118 +/- 21 milliseconds, respectively; P < 0.01), whereas the E wave deceleration times (DT) were alike in both apparently healthy and unhealthy subjects. The diastolic and systolic components of the pulmonary venous blood flow were alike in apparently healthy and unhealthy subjects. Left atrial size was increased in all patients with disease, possibly indicating increased preload. CONCLUSION: In this population sample of elderly men, the commonly used E/A ratio did not distinguish between apparently healthy subjects and those with cardiovascular diseases such as CHD or hypertension, which are known to be associated with LV diastolic dysfunction in the middle-aged population. IVRT appeared to be the most sensitive of the Doppler-derived indices of LV diastolic function used in the present study, but for this variable, the differences between apparently healthy subjects and unhealthy subjects were small. Thus, the age-associated changes in LV compliance appear to override the impact of these disorders on indices of LV diastolic function in elderly populations.

Left Ventricular Systolic Function in a Population Sample of Elderly Men

BACKGROUND: The present study was designed to evaluate the usefulness and discriminatory power of different echocardiographic indices of left ventricular (LV) systolic function in a healthy screening sample of 584 men who were 70 years old. METHODS: Ejection fraction (EF), fractional shortening (FS), stroke index (SI), left ventricular diameter in systole (LVESD), and cardiac index (CI) were evaluated, in addition to LV wall motion score and atrioventricular plane displacement (AVPD). RESULTS: Subjects with hypertension or coronary heart disease (CHD), but not those with diabetes mellitus, showed impairments in EF, FS, LVESD, AVPD, and LV wall motion scores compared with the healthy subjects in the sample (P < 0.01-0.001). SI and CI findings in those with hypertension or CHD were, however, no different from those in the healthy group. The index of LV systolic function that discriminated best between diseased and healthy subjects was LV wall motion score, being correlated with EF, LVESD, and AVPD but only poorly with SI and CI. SI evaluated with use of the Teichholz formula was correlated to LV end-diastolic diameter (r = 0.72, P < 0.0001), whereas the corresponding correlation between SI measured with Doppler (aortic flow) and LVEDD was weak. The difference between the Teichholz and Doppler evaluations of SI was dependent on LV end-diastolic diameter (r = 0.51, P < 0.001) but not on LV systolic function. An index, the systolic two-dimensional index, which takes into account both the longitudinal motion (AVPD) and movement along the short axis (LVESD) during systole, was suggested by the formula AVPD + 5/LVESD. CONCLUSIONS: Impaired LV systolic function was found in both elderly men with hypertension and those with CHD. SI was normal in these groups, however, although overestimated when measured with the Teichholz formula in this population with a large proportion of subjects with LV dilatation. AVPD appears to be applicable in the present population, and a new systolic index consisting of LVESD and AVPD is suggested for the evaluation of LV systolic function in two dimensions.

Repeated vital capacity manoeuvres after cardiopulmonary bypass: effects on lung function in a pig model

Respiratory failure following cardiopulmonary bypass (CPB) is a major complication after cardiac surgery. A vital capacity inflation of the lungs, performed before the end of CPB, may improve gas exchange, but the necessity to repeat it is unclear. Therefore, we studied 18 pigs undergoing hypothermic CPB. A vital capacity manoeuvre (VCM) was performed in two groups and consisted of inflating the lungs for 15 s to 40 cm H2O at the end of CPB. In one group, VCM was repeated every hour. The third group served as controls. Atelectasis was studied by CT scan. Intrapulmonary shunt increased after bypass in the controls and improved spontaneously 3 h later without returning to baseline values. From 3 to 6 h after CPB, there was no more improvement and more than 10% atelectasis remained at 6 h. In contrast, the two groups treated before termination of CPB with VCM showed only minor atelectasis and no abnormal changes in gas exchange directly after bypass or later. We conclude that the protective effect of VCM remained for 6 h after bypass, and there was no extra benefit on gas exchange by repeating the VCM.

Individual lung blood flow during unilateral hypoxia: effects of inhaled nitric oxide

We hypothesized that the diversion of blood away from a hypoxic lung to the opposite oxygenated lung can be enhanced by inhaling nitric oxide (NO) into the oxygenated lung. We measured individual lung blood flow when 50 ppm NO was selectively inhaled to: a hyperoxic lung during contralateral hypoxia; a normoxic lung during bilateral normoxia; and a hyperoxic lung during bilateral hyperoxia. Twenty two patients with healthy lungs were studied during intravenous anaesthesia. The lungs were separately and synchronously ventilated. The relative perfusion of each lung was assessed by the inert gas elimination technique. Unilateral hypoxic (inspiratory oxygen fraction (FI,O2) 0.05) ventilation during contralateral hyperoxia reduced the perfusion of the hypoxic lung from a mean (SD) of 47 (9)% of cardiac output (Q'), to 30 (7)% (p<0.001) of Q'. NO inhalation to the hyperoxic lung increased its blood flow from 70 (7)% to 75 (6)% (p<0.05) of Q', and reduced the blood flow to the hypoxic lung to 25 (6)% (p<0.05). Unilateral NO inhalation during bilateral normoxia or hyperoxia had no effect on pulmonary blood flow distribution. Nitric oxide inhalation to a hyperoxic lung increases the perfusion to this lung by redistribution of blood flow if the opposite lung is hypoxic.

Acute effects of continuous rotational therapy on ventilation-perfusion inequality in lung injury

OBJECTIVE

To investigate ventilation-perfusion (VA/Q) relationships, during continuous axial rotation and in the supine position, in patients with acute lung injury (ALI) using the multiple inert gas elimination technique.

DESIGN

Prospective investigation.

SETTING

Eighteen-bed intensive care unit in a university hospital.

PATIENTS AND INTERVENTIONS

Ten patients with ALI (PaO2/FIO2 ratio < 300 mm Hg) were mechanically ventilated in a pressure controlled mode and placed on a kinetic treatment table.

MEASUREMENTS AND RESULTS

Distributions of VA/Q were determined 1) during rotation (after a period of 20 min) and 2) after a resting period of 20 min in the supine position. During axial rotation, intrapulmonary shunt (19.1 +/- 15% of cardiac output) was significantly reduced in comparison with when in the supine position (23 +/- 14%, p < 0.05), areas with "low" VA/Q were not affected by the positioning maneuver. General VA/Q mismatch (logarithmic distribution of pulmonary blood flow) was decreased during rotation (0.87 +/- 0.37) in comparison with when the patient was in the supine position (0.93 +/- 0.37, p < 0.05). Arterial oxygenation was significantly improved during continuous rotation (PaO2/FIO2 = 217 +/- 137 mm Hg) as compared with in the supine position (PaO2/FIO2 = 174 +/- 82 mm Hg, p < 0.05). The positive response of the continuous rotation on arterial oxygenation was only demonstrated in patients with a Murray Score of 2.5 or less, indicating a "mild to moderate" lung injury, while in patients presenting with progressive ARDS (Murray Score > 2.5), the acute positive response was limited.

CONCLUSIONS

Continuous axial rotation might be a method for an acute reduction of VA/Q mismatch in patients with mild to moderate ALI, but this technique is not effective in late or progressive ARDS. Further studies including a large data collection are needed.

Use of a vital capacity maneuver to prevent atelectasis after cardiopulmonary bypass: an experimental study

BACKGROUND

Respiratory failure secondary to cardiopulmonary bypass (CPB) remains a major complication after cardiac surgery. The authors previously found that the increase in intrapulmonary shunt was well correlated with the amount of atelectasis. They tested the hypothesis that post-CPB atelectasis can be prevented by a vital capacity maneuver (VCM) performed before termination of the bypass.

METHODS

Eighteen pigs received standard hypothermic CPB (no ventilation during bypass). The VCM was performed in two groups and consisted of inflating the lungs during 15 s to 40 cmH2O at the end of the bypass. In one group, the inspired oxygen fraction (FIO2) was then increased to 1.0. In the second group, the FIO2 was left at 0.4. In the third group, no VCM was performed (control group). Ventilation-perfusion distribution was measured with the inert gas technique and atelectasis by computed tomographic scanning.

RESULTS

Intrapulmonary shunt increased after bypass in the control group (from 4.9 +/- 4% to 20.8 +/- 11.7%; P < 0.05) and was also increased in the vital capacity group ventilated with 100% oxygen (from 2.2 +/- 1.3% to 6.9 +/- 2.9%; P < 0.01) but was unaffected in the vital capacity group ventilated with 40% oxygen. The control pigs showed extensive atelectasis (21.3 +/- 15.8% of total lung area), which was significantly larger (P < 0.01) than the proportion of atelectasis found in the two vital capacity groups (5.7 +/- 5.7% for the vital capacity group ventilated with 100% oxygen and 2.3 +/- 2.1% for the vital capacity group ventilated with 40% oxygen.

CONCLUSION

In this pig model, postcardiopulmonary bypass atelectasis was effectively prevented by a VCM.

Atelectasis is a major cause of hypoxemia and shunt after cardiopulmonary bypass: an experimental study

BACKGROUND

Respiratory failure after cardiopulmonary bypass (CPB) remains a major complication after cardiac surgery. The authors tested the hypothesis that atelectasis is an important factor responsible for the increase in intrapulmonary shunt after CPB.

METHODS

Six pigs received standard CPB (bypass group). Six other pigs had the same surgery but without CPB (sternotomy group). Another six pigs were anesthetized for the same duration but without any surgery (control group). The ventilation-perfusion distribution was measured with the inert gases technique, extravascular lung water was quantified by the double-indicator distribution technique, and atelectasis was analyzed by computed tomography.

RESULTS

Intrapulmonary shunt increased markedly after bypass but was unchanged over time in the control group (17.9 +/- 6.2% vs. 3.5 +/- 1.2%; P < 0.0001). Shunt also increased in the sternotomy group (10 +/- 2.6%; P < 0.01 compared with baseline) but was significantly lower than in the bypass group (P < 0.01). Extravascular lung water was not significantly altered in any group. The pigs in the bypass group showed extensive atelectasis (32.3 +/- 28.7%), which was significantly larger than in the two other groups. The pigs in the sternotomy group showed less atelectasis (4.1 +/- 1.9%) but still more (P < 0.05) than the controls (1.1 +/- 1.6%). There was good correlation between shunt and atelectasis when all data were pooled (R2 = 0.67; P < 0.0001).

CONCLUSIONS

Atelectasis is produced to a much larger extent after CPB than after anesthesia alone or with sternotomy and it explains most of the marked post-CPB increase in shunt and hypoxemia. Surgery per se contributes to a lesser extent to postoperative atelectasis and gas exchange impairment.

Effect of thoracic epidural anaesthesia on ventilation-perfusion distribution and intrathoracic blood volume before and after induction of general anaesthesia

BACKGROUND

Gas exchange is impaired during general anaesthesia due to development of shunt and ventilation-perfusion mismatching. Thoracic epidural anaesthesia (TEA) may affect the mechanics of the respiratory system, intrathoracic blood volume and possibly ventilation-perfusion (VA/Q) distribution during general anaesthesia.

METHODS

VA/Q relationships were analyzed in 24 patients undergoing major abdominal surgery. Intrapulmonary shunt (Qs/QT), perfusion of "low" VA/Q areas, ventilation of "high" VA/Q regions, dead space ventilation and mean distribution of ventilation and perfusion were calculated from the retention/excretion data of six inert gases. Intrathoracic blood volume (ITBV) and pulmonary blood volume (PBV) were determined with a double indicator technique. Recordings were made before and after administration of 8.5 +/- 1.5 ml bupivacaine 0.5% (n = 12) or 8.3 +/- 1.8 ml placebo (n = 12) into a thoracic epidural catheter and after induction of general anaesthesia.

RESULTS

Before TEA, Qs/QT was normal in the bupivacaine group (2 +/- 2%) and the placebo group (2 +/- 3%). TEA covering the dermatomal segments T 12 to T 4 had no effect on VA/Q relationships, ITBV and PBV. After induction of general anaesthesia Qs/QT increased to 8 +/- 4% (bupivacaine group, P < 0.05 and to 7 +/- 2% (placebo group, P < 0.05). ITBV and PBV decreased significantly to the same extent in the bupivacaine group and the placebo group.

CONCLUSIONS

TEA has no effect on VA/Q distribution, gas exchange and intrathoracic blood volume in the awake state and does not influence development of Qs/QT and VA/Q inequality after induction of general anaesthesia.

The ventilation-perfusion relation and gas exchange in mitral valve disease and coronary artery disease. Implications for anesthesia, extracorporeal circulation, and cardiac surgery

BACKGROUND

Patients with mitral valve disease (MVD) are at greater risk for respiratory complications after cardiac surgery compared with patients with coronary artery disease (CAD). The authors hypothesized that ventilation-perfusion (VA/Q) inequality is more pronounced in patients with MVD before and after induction of anesthesia and during and after surgery when extracorporeal circulation (ECC) is used.

METHODS

In patients with MVD (n = 12) or with CAD (n = 12), VA/Q distribution was determined using the multiple inert gas elimination technique. Intrapulmonary shunt (Qs/Qr) defined as regions with VA/Q < 0.005 [% of total perfusion (Qr)], perfusion of "low" VA/Q areas (0.005 < or = VA/Q < 0.1, [% of Qr]), ventilation of "high" VA/Q regions (10 < or = VA/Q < or = 100 [% of total ventilation VE]), and dead space (VA/Q > 100 [% of VE]) were calculated from the retention/excretion data of the inert gases. Recordings were obtained while patients spontaneously breathed air in the awake state, during mechanical ventilation after induction of anesthesia, after separation of patients from ECC, and 4 h after operation.

RESULTS

Qs/Qr was low in the awake state (MVD group, 3% +/- 3%; CAD group, 3% +/- 4%) and increased after induction of anesthesia to 10% +/- 8% (MVD group, P < 0.05) and 11% +/- 7% (CAD group, P < 0.01). Qs/Qr increased further after separation from ECC (MVD group, 24% +/- 9%, P < 0.01; CAD group, 23% +/- 7%, P < 0.01). Similarly, alveolar-arterial oxygen tension difference (PA-aO2) increased from 168 +/- 54 mmHg (anesthetized state) to 427 +/- 138 mmHg after ECC (MVD group, P < 0.01) and from 153 +/- 65 mmHg to 377 +/- 101 mmHg (CAD group, P < 0.01). In both groups, PA-aO2 was correlated with Qs/Qr. Four hours after operation, Qs/Qr had decreased significantly to 8% +/- 6% (CAD group) and 10% +/- 6% (MVD group). PA-aO2 and Qs/Qr showed no significant differences between the CAD and MVD groups.

CONCLUSIONS

Qs/Qr is the main pathophysiologic mechanism of gas exchange impairment during cardiac surgery for MVD or CAD. Impairment of pulmonary gas exchange secondary to general anesthesia, cardiac surgery, and ECC are comparable for patients undergoing myocardial revascularization or mitral valve surgery.

Central and regional hemodynamics during acute hypovolemia and volume substitution in volunteers

OBJECTIVES

To study the central and regional hemodynamics and oxygen consumption during acute hypovolemia and volume replacement with crystalloid and colloid solutions.

DESIGN

Prospective, randomized, laboratory investigation.

SETTING

Clinical physiology department at a university hospital.

SUBJECTS

Eighteen healthy male volunteers, between 21 and 35 yrs of age (mean 26).

INTERVENTIONS

Catheters were inserted in the cubital vein, brachial artery, pulmonary artery, thoracic aorta, right hepatic vein, and left renal vein for measurements of systemic arterial and pulmonary arterial pressures, total and central blood volumes, extravascular lung water, and the splanchnic (liver) and renal blood flow rates. The exchange of respiratory gases was measured, using the Douglas bag technique. Measurements were made before and after a venesection of 900 mL and again after the subjects had been randomized and received volume replacement with either 900 mL of Ringer's acetate solution 900 mL of albumin 5%, or 900 plus 900 mL of Ringer's solution.

MEASUREMENTS AND MAIN RESULTS

Withdrawal of 900 mL of blood decreased cardiac output and the splanchnic and renal blood flow rates by between -16% and -20%. The oxygen uptake decreased by 13% in the whole body, while it remained unchanged in the liver and kidney. The systemic and pulmonary vascular resistances increased, while the extravascular lung water decreased. Autotransfusion of fluid from tissue to blood was indicated by hemodilution, which was most apparent in subjects showing only a minor change in peripheral resistance. Cardiac output, blood volume, and systemic vascular resistance were significantly more increased by infusion of 900 mL of albumin 5% than by 900 mL of Ringer's solution. However, infusion of 1800 mL of Ringer's solution increased the extravascular lung water and the pulmonary arterial pressures to significantly above baseline, while no significant difference from baseline was found after 900 mL of Ringer's acetate solution.

CONCLUSIONS

Withdrawal of 900 mL of blood induces similar reductions in cardiac output as in the splanchnic and renal blood flow rates. A fluid shift from the extravascular to the intravascular fluid compartment might restore up to 50% of the blood loss. Optimal volume substitution with Ringer's solution can be effectuated by infusing between 100% and 200% of the amount of blood lost.

Haemodynamics during inhalation of a 50% nitrous-oxide-in-oxygen mixture with and without hypovolaemia

BACKGROUND

Inhalation of a gas mixture containing 50% nitrous oxide in oxygen (N2O/O2) is widely used for pain relief in emergency situations, which may also be associated with blood loss. The aim of this study was to evaluate the haemodynamic effects of this gas mixture in normo- and hypovolaemic subjects.

METHODS

Six healthy males were studied during inhalation of N2O/O2 before and after withdrawal of 900 ml of blood. On each occasion, we measured systemic and pulmonary arterial pressures, cardiac output, blood gases, extravascular lung water, and the blood flow and oxygen consumption in the whole body, liver and kidneys.

RESULTS

Inhalation of N2O/O2 reduced the stroke volume and increased peripheral resistance. Oxygen uptake decreased in the liver (-30%) and in the whole body (-23%). Blood withdrawal reduced the pulmonary arterial and central venous pressures (-30 to -50%) and further decreased stroke volume and the blood flows to the liver and the kidney (-15%). The extravascular lung water tended to increase both during inhalation of N2O/O2 and during hypovolaemia.

CONCLUSION

N2O/O2 aggravated the hypokinetic circulation induced by hypovolaemia. However, the oxygen consumption decreased only during inhalation of N2O/O2. This opens up the possibility that the cardiodepression associated with N2O/O2 is caused by a change in metabolic demands.

Hypoxic pulmonary vasoconstriction in human lungs. A stimulus-response study

BACKGROUND

A stimulus-response relation between alveolar oxygen tension and pulmonary vascular resistance has been observed in animals. This study investigated this relation in healthy human lungs. The distribution of pulmonary blood flow was measured during unilateral (1) graded hypoxia (fractional concentration of oxygen in inspired gas [FIO2] = 0.12, 0.08, and 0.05) and contralateral hyperoxia (FIO2 = 1.0; n = 6); (2) single-step hypoxia (FIO2 = 0.05) and contralateral hyperoxia (n = 5); and (3) normobaric hyperoxia and contralateral normoxia (FIO2 = 0.25; n = 6).

METHODS

Seventeen patients with healthy lungs were studied during intravenous anesthesia. The lungs were separately and synchronously ventilated. The relative perfusion of each lung was assessed by the inert gas (sulfurhexafluoride) elimination technique.

RESULTS

(1) Unilateral graded hypoxia reduced the perfusion of the hypoxic lung from a mean (+/-SD) of 52 (2)% of cardiac output (Q) during bilateral hyperoxia, to 47 (5)% (P > 0.05) 40 (3)% (P < 0.01), and 30 (8)% (P < 0.001) of Q, respectively. These progressive reductions in the perfusion of the hypoxic lung were all significantly different from each other. (2) Unilateral single-step hypoxia caused a blood flow diversion of the same magnitude as when the lung was previously ventilated with FiO2 of 0.12 and 0.08. The perfusion of the hypoxic lung was reduced from 46 (9)% of Q (bilateral hyperoxia) to 26 (4)% of Q (P < 0.01). (3) Unilateral hyperoxia did not significantly change the relative blood flow distribution between the two lungs or the pulmonary artery pressure.

CONCLUSIONS

A stimulus-response relation between graded hypoxia and blood flow diversion defines hypoxic pulmonary vasoconstriction in the normal human lung. Hyperoxia has no significant effect on vascular resistance in the normal human lung.

A comparison of pressure- and volume-controlled ventilation at different inspiratory to expiratory ratios

BACKGROUND

Inverse ratio ventilation (IRV) is frequently used in severe acute respiratory failure. IRV may lead to intrinsic positive end-expiratory pressure (PEEP) and is thought to improve oxygenation and to have advantageous effects on lung mechanics. Published data to support the use of IRV are scarce. This animal study compares external PEEP with intrinsic PEEP in pressure- and volume-controlled ventilation.

METHODS

Fifteen pigs were randomly treated with 1. volume-controlled PEEP ventilation (I:E ratio 1:2) (VCV PEEP), 2. volume-controlled ventilation (I:E ratio 4:1) (VCIRV) and 3. pressure-controlled ventilation (I:E ratio 4:1) (PCIRV). Baseline measurements were performed using volume-controlled ventilation (I:E ratio 1:2) (VCV ZEEP). Lung mechanics, haemodynamics and gas exchange were measured by standard methods and functional residual capacity (FRC) by the sulphur hexafluoride technique.

RESULTS

In comparison to VCV PEEP, PCIRV resulted in reduced peak airway pressure (32 +/- 3 vs. 27 +/- 6 cm H2O, P < 0.001) and increased mean airway pressure (14 +/- 2 vs. 22 +/- 5 cm H2O, P < 0.001). FRC was 942 +/- 264 ml in VCV PEEP and 1024 +/- 390 ml in PCIRV (n.s.). Oxygen delivery was lower in PCIRV (458 +/- 193 vs. 346 +/- 150 ml/min, P < 0.05). Physiologic dead space was 14 +/- 4% in PCIRV and 20 +/- 6% in VCV PEEP and VCIRV (P < 0.005).

CONCLUSIONS

Inverse ratio ventilation did not result in improved FRC in comparison to conventional volume-controlled PEEP ventilation. PCIRV allows for a reduction in minute ventilation but the increase in mean airway pressure compromises circulation.

Nebulisation of hypertonic saline causes oedema of the airway wall

The effect of aerosol challenge with distilled water, and with isotonic and hypertonic saline on the respiratory system of the anaesthetized rabbit was investigated. Nebulisation of hypertonic (3.6%) saline caused an increase in the extravascular lung water without altering the total body weight. Morphometrical investigations revealed an increase of the subepithelial tissue compartment (connective tissue and smooth muscle) of the airway wall. X-ray microanalysis showed higher content of Na, K, and Cl in this compartment already 10 min after nebulisation of hypertonic saline. The formation of oedema was associated with a significant decrease in both compliance and gas exchange.

Left ventricular hypertrophy and geometry in a population sample of elderly males

BACKGROUND

Recent studies have shown that left ventricular geometric adaptation to hypertension is complex. The spectrum of geometric adaptations in a general population and its relationship to systolic and diastolic function has, however, not been investigated.

OBJECTIVES AND METHODS

This echocardiographic and Doppler study investigated the relationships between left ventricular geometric shape (normal, concentric remodelling, concentric hypertrophy and eccentric hypertrophy) and left ventricular systolic and diastolic function in a population sample of 584 males aged 70 in Uppsala, Sweden. The influences of hypertension, coronary heart disease and diabetes mellitus were also evaluated.

RESULTS

Sixteen percent of the healthy population (n = 167) demonstrated the presence of left ventricular hypertrophy (mainly eccentric). Subjects with hypertension (n = 115) showed an increased left ventricular mass (eccentric left ventricular hypertrophy 31%, concentric left ventricular hypertrophy 15%), when compared with healthy subjects (P < 0.001). Subjects with coronary heart disease (n = 32) without hypertension also showed an increased left ventricular mass (most often eccentric) (P < 0.05). Using Doppler determinations of cardiac index, no differences were found in cardiac index between the geometric groups. Raised total peripheral resistance, increased blood pressure and enlarged left atrium were found in both concentric and eccentric left ventricular hypertrophy (P < 0.01-0.05). Disturbed diastolic function was seen with a prolongation of the isovolumic relaxation time in eccentric (P < 0.01) and increased atrial-dependent left ventricular filling in concentric left ventricular hypertrophy (P < 0.05).

CONCLUSION

Alterations in left ventricular geometry were common in this population-based study of elderly males, both in healthy subjects and in subjects with hypertension or coronary heart disease. Raised total peripheral resistance and left ventricular diastolic dysfunction were common findings in both concentric and eccentric left ventricular hypertrophy.

V/Q distribution and correlation to atelectasis in anesthetized paralyzed humans

Regional ventilation and perfusion were studied in 10 anesthetized paralyzed supine patients by single-photon emission computerized tomography. Atelectasis was estimated from two transaxial computerized tomography scans. The ventilation-perfusion (V/Q) distribution was also evaluated by multiple inert gas elimination. While the patients were awake, inert gas V/Q ration was normal, and shunt did not exceed 1% in any patient. Computerized tomography showed no atelectasis. During anesthesia, shunt ranged from 0.4 to 12.2. Nine patients displayed atelectasis (0.6-7.2% of the intrathoracic area), and shunt correlated with the atelectasis (r = 0.91, P < 0.001). Shunt was located in dependent lung regions corresponding to the atelectatic area. There was considerable V/Q mismatch, with ventilation mainly of ventral lung regions and perfusion of dorsal regions. Little perfusion was seen in the most ventral parts (zone 1) of caudal (diaphragmatic) lung regions. In summary, shunt during anesthesia is due to atelectasis in dependent lung regions. The V/Q distributions differ from those shown earlier in awake subjects.

Inhalation of a nitric oxide synthase inhibitor to a hypoxic or collapsed lung lobe in anaesthetized pigs: effects on pulmonary blood flow distribution

I.v. administration of the nitric oxide synthase inhibitor, nitro-L-arginine methyl ester (L-NAME), not only reduces blood flow in a hypoxic lung region but also causes systemic vasoconstriction and a decrease in cardiac output. In this study, we delivered nebulized L-NAME 0.2-1 mg kg-1 to the left lower lobe of 10 anaesthetized pigs. The left lower lobe was made hypoxic by selective inhalation of 5% oxygen or collapsed by interrupted ventilation, or both. Inhalation of L-NAME reduced fractional blood flow to the left lower lobe from 5.3 (SD 3.1)% to 1.7 (1.4)% (P < 0.05) in lobar hypoxia and from 6.0 (3.3) to 2.7 (2.7)% (P < 0.05) in lobar collapse. These reductions were accompanied by a significant increase in PaO2. There were no significant changes in arterial pressure, cardiac output or heart rate. We have shown that selective inhalation of L-NAME reduced blood flow to a hypoxic or collapsed lung region without systemic effects. The possible role for nitric oxide synthase inhibition in reducing shunt during one-lung ventilation, however, requires further study.

Pulmonary epithelial permeability. An animal study of inverse ratio ventilation and conventional mechanical ventilation

STUDY OBJECTIVE

To compare pressure-controlled inverse ratio ventilation (PCIRV) with volume-controlled ventilation with positive end-expiratory pressure (VCV PEEP) at equal levels of end-expiratory alveolar pressure. The primary focus of the study was on pulmonary epithelial permeability. Histologic and gravimetric indicators of lung injury were also studied.

DESIGN

Randomized animal study.

SETTING

Experimental investigation at Södersjukhuset, Stockholm, Sweden.

ANIMALS

Thirty-two New Zealand white rabbits.

INTERVENTIONS

Ventilation with PCIRV or VCV PEEP for 6 h at an end-expiratory pressure level of 5 cm H2O.

MEASUREMENTS AND RESULTS

Lung mechanics, heart rate, BP, and gas exchange. Measurement of pulmonary epithelial permeability by 99mTc-DTPA lung clearance. Extravascular lung water by gravimetric analysis. Morphology by light microscopy after a perfusion fixation procedure. Mean and peak airway pressures were 12.4 +/- 4.3 and 15.9 +/- 4.5 cm H2O with PCIRV and 8.6 +/- 0.8 (p < 0.001) and 19.9 +/- 4.1 cm H2O (p < 0.03) with VCV PEEP at 6 h. Mean systemic BP was lower with PCIRV (58 +/- 9 mm Hg) than with VCV PEEP (68 +/- 7 mm Hg) at 6 h (p < 0.003). At 6 h, PaCO2 was lower with PCIRV (3.2 +/- 0.6 kPa) than with VCV PEEP (4.1 +/- 0.8 kPa) (p < 0.02). There was no difference in blood oxygenation between PCIRV and VCV PEEP. 99mTc-DTPA lung clearance curves were monoexponential with both PCIRV and VCV PEEP. Mean lung clearance expressed as T 1/2 was 16 +/- 9 min with PCIRV and 107 +/- 74 min with VCV PEEP (p < 0.001). Morphologic examination revealed no differences between the groups and no evidence of significant lung injury.

CONCLUSIONS

The observations reported in this article imply that PCIRV causes an alteration in lung epithelial or membrane function in comparison to VCV PEEP. This functional difference is most likely caused by the large time-adjusted lung volume produced by pressure control in combination with a prolonged inspiration. It remains to be established whether this early functional effect of PCIRV is relevant with regard to structural lung injury in mechanically ventilated subjects.

Lung aeration. The effect of pre-oxygenation and hyperoxygenation during total intravenous anaesthesia

We have investigated the effect of pre-oxygenation and hyperoxygenation (an increase in inspired oxygen fraction from 0.4 to 1.0 after induction of general anaesthesia) on aeration and atelectasis formation in the lungs during total intravenous anaesthesia. Twenty-seven consecutive patients were randomly allocated to group 1 (with pre-oxygenation), group 2 (without pre-oxygenation), or group 3 (hyperoxygenation). Lung aeration was investigated by means of spiral computed tomography. The aeration of lung regions identified by computed tomography scans was divided into five categories: over-aeration, normal aeration, reduced aeration, poor aeration, and atelectasis formation. In group 1 larger areas of atelectasis were found in the basal parts of the lungs compared to group 2. In group 3 a significant increase in atelectatic areas with a corresponding reduction in areas with reduced aeration occurred at the bases of the lungs. The considerable increase in atelectasis associated with pre-oxygenation and its rapid appearance during hyperoxygenation suggest that these procedures should be used with caution.

Volumetric analysis of aeration in the lungs during general anaesthesia

Spiral computed tomography (CT) allows volumetric analysis of formation of atelectasis and aeration of the lungs during anaesthesia. We studied 26 premedicated patients undergoing elective surgery allocated to group 1 (conscious, spontaneous breathing, investigating inspiration and expiration), group 2 (general anaesthesia with mechanical ventilation, investigating inspiration and expiration) or group 3 (general anaesthesia with mechanical ventilation, investigating changes over time). Using spiral CT, the lungs were studied either before or during general anaesthesia. CT scans were grouped into the following areas: overaeration, normal aeration, reduced aeration, poor aeration and atelectasis. The mechanism of atelectasis appeared to be both gravitational forces and a diaphragm-related force that acts regionally in caudal lung regions. Mean atelectasis formation and poorly aerated regions comprised approximately 4% of the total lung volume between the diaphragm and carina, giving a mean value of 16-20% of the normal aerated lung tissue being either collapsed or poorly aerated. The vertical ventilation distribution was more even during anaesthesia than in the awake state.

Gas exchange, expiratory flow obstruction and the clinical spectrum of asthma

More than any other chronic respiratory disease, asthma is characterized by functional and clinical variability: expiratory flow obstruction, dyspnoea and wheezing may be absent, mild, or severe. Moreover, pulmonary gas exchange often does not closely relate to measured airway obstruction. Accordingly, the correlation between arterial oxygen tension and airflow (Pa,O2) rate indices of obstruction is poor, both in a single patient over time, and within groups of clinically similar patients. Here, these concepts are extended by examining relationships between airflow obstruction and gas exchange across the clinical spectrum of asthma (from asymptomatic to acute severe). Six individual studies encompassing 86 patients are analysed together, focusing on: 1) airways obstruction; 2) arterial blood gas data; and 3) the distribution of alveolar ventilation/perfusion (V'A/Q') ratios, measured by the multiple inert gas elimination technique. V'A/Q' mismatching was greater than normal even when forced expiratory volume in one second (FEV1) was normal, but with increasing severity of airways obstruction there was essentially no further deterioration in gas exchange until FEV1 reached about 40% of predicted normal values. Then, with little further airways obstruction, gas exchange rapidly worsened, Pa,O2 falling to about 50 torr. This study emphasizes that what has been observed in individual patients and within clinically similar patient groups can be extended across the spectrum of asthma severity: airways obstruction and gas exchange are poorly correlated. Furthermore, these results suggest that spirometric data alone may not adequately define remission, nor clearly identify those patients liable to serious gas exchange deterioration.