Ventilatory efficiency during exercise in healthy subjects

When evaluating dyspnea in patients with heart or lung disease it is useful to measure the quantity of ventilation needed to eliminate metabolically produced CO2 (i.e., the ventilatory efficiency). Mathematically, the relationship between ventilation (VE) and CO2 output is determined by the arterial CO2 pressure and the physiologic dead space-tidal volume ratio. We decided to determine how age, sex, size, fitness, and the type of ergometer influenced ventilatory efficiency in normal subjects. Three methods were compared for expressing this relationship: (1) the VE versus CO2 output slope below the ventilatory compensation point, commonly used by cardiologists for estimating the severity of heart failure; (2) the VE/CO2 output ratio at the anaerobic threshold, commonly used by pulmonologists; and (3) the lowest VE/CO2 output ratio during exercise, the latter parameter not previously reported. We studied 474 healthy adults, between 17 and 78 years of age during incremental cycle and treadmill cardiopulmonary exercise tests at three test sites, correcting the total VE for the equipment dead space. The lowest VE/CO2 output ratio was insignificantly different from the ratio at the anaerobic threshold, less variable than that for the slope relationship, and unaffected by the site, ergometer, and gas exchange measurement systems. The regression equation for the lowest VE/CO2 output ratio was 27.94 + 0.108 x age + (0.97 = F, 0.0 = M) - 0.0376 x height, where age is in years and height is in centimeters. We conclude that the lowest VE/CO2 output ratio is the preferred noninvasive method to estimate ventilatory inefficiency.     

Changes in general haemodynamics and renal function during exercise in patients with arterial hypertension.

Basic haemodynamic parameters were measured in 58 men in various stages of essential hypertension, 18 patients with hypertensive form of chronic glomerulonephritis, and 23 practically healthy persons during graded exercise in the supine position on a bicycle ergometer for 30 minutes. During exercise, the systolic pressure rose in all persons investigated, whereas the diastolic pressure markedly increased only in patients with arterial hypertension. The cardiac index increased, according to the intensity of the exercise equally in the healthy persons and in patients in early stages of essential hypertension; a lesser increase in the cardiac index was observed in patients in late stages of hypertension and in those with chronic glomerulonephritis. The increase in the cardiac index during exercise is essentially due to an increase in the heart rate; the stroke index increases only slightly, and in later stages of essential hypertension even decreases. The total peripheral resistance diminishes during exercise, but less so in patients with arterial hypertension in whom it is distinctly higher than in healthy persons. The circulating blood volume decreases during exercise in consequence of a decrease in plasma volume, whereas the haematocrit value increases. Renal blood flow and glomerular filtration decrease during exercise, both in healthy untrained persons and in patients with arterial hypertension. In patients in late stages of essential hypertension and in those with glomerulonephritis, the above parameters decrease more markedly and at lower exercise intensity than in healthy persons.     

Changes in plasma proenkephalin peptide F and catecholamine levels during graded exercise in men.

Proenkephalin peptide F immunoreactivity, epinephrine, and norepinephrine were measured in the plasma of endurance-trained and untrained male subjects riding on a bicycle ergometer at 28%, 54%, 83%, and 100% of maximum oxygen consumption (VO2). At rest the trained group had peptide F levels almost twice the level of the untrained group, whereas all other variables measured were the same. The maximum epinephrine and norepinephrine levels were found at 100% exercise intensity, with a precipitous drop in the levels at 5 min of recovery. In contrast, the peptide F immunoreactivity reached a maximum at 5 min of recovery and was still substantially above the initial level after 15 min of rest. In addition, the trained subjects showed another peak of peptide F immunoreactivity at 54% VO2max. Possible explanations for the different patterns of catecholamine and peptide F levels are presented.     

Changes in arterial plasma potassium and ventilation during exercise in man

We have investigated the relationship between arterial plasma potassium ( [K+]a) and ventilation (VE) in man because hyperkalaemia has been shown to increase VE in the anaesthetized cat by direct stimulation of the arterial chemoreceptors. Six healthy male volunteers undertook about of sub-maximal (100 W) and maximal (sprint ca. 350 W) exercise on a cycle ergometer. VE was measured breath-by-breath and arterial blood was sampled at regular intervals from a catheter inserted into a brachial artery for measurement of [K+]a and base excess. Changes in [K+]a closely mirrored changes in VE during exercise and recovery. At 100 W [K+]a increased from 4 mM to 5 mM, and during the sprint [K+]a increased to ca. 7 mM. Base excess did not mirror VE in that it reached its nadir 1-3 min after exercise had stopped, when [K+]a and VE were both falling. The increases in [K+]a seen here are probably sufficient to enhance the arterial chemoreceptor drive during exercise. Furthermore, the close temporal relationship between [K+]a and VE suggests that it is possible that exercise hyperkalaemia may contribute to the control of breathing in exercise.     

On the boundary conditions used in calculations of gas mixing in alveolar lungs.

The lung boundaries exhibit a tight barrier for any insoluble gas; hence boundary conditions for lung gas mixing have to account for the absence of both diffusive and convective fluxes across the lung walls. Scrimshire et al. (1978) have, in contrast, used the less rigid boundary condition that only the net flux be zero. As we believe this boundary condition to be inappropriate for the study of insoluble gases, the results derived appear to have no physiological significance.     

Changes in echocardiographic left ventricular minor axis dimensions during exercise in patients with aortic stenosis.

Twelve patients with aortic stenosis (gradient 62 (25) mm Hg), and six normal subjects were examined using M mode echocardiography before and during submaximal bicycle exercise. Normal subjects showed a progressive fall in the end systolic minor axis dimension of the left ventricle and a rise in end diastolic dimension, giving an increase in stroke dimension and shortening fraction of 45% and 37% respectively at peak exercise. Patients with aortic stenosis showed no consistent alteration in either end systolic or end diastolic dimension, and consequently stroke dimension was unchanged during exercise. None of the patients with an abnormal exercise response had evidence of left ventricular failure at rest, and all but one completed the exercise protocol without undue dyspnoea. Non-invasive exercise testing in patients with aortic stenosis may detect abnormalities of left heart function which are not apparent at rest. These abnormalities may provide early evidence either of severe aortic stenosis or of incipient left ventricular failure.     

Estimating alveolar surface area during life.

Alveolar surface area (Sa) may be derived from measurements of total lung capacity (TLC) and mean linear intercept (Lm), an estimate of average airspace size. Because the index of pulmonary distensibility, K, is a function of Lm, we were able to derive Lm from ln K using their respective age regressions and estimated Sa in 147 healthy subjects. K was obtained from exponential analysis of static pressure-volume data. TLC was measured in a body plethysmograph. As an estimate of airspace size, the value used for Lm was shown to be appropriate for the air-inflated lung at TLC. In 95 men (mean age 40 +/- 16 SD years), Sa was 118 (SD 22) m2 and in 52 women (mean age 38 +/- 17 SD years) it was 91 (SD 18) m2 and Sa decreased with age (P less than 0.001). In a morphometric study, Thurlbeck (Am. Rev. Respir. Dis. 95: 765-773, 1967) obtained smaller values for Sa (owing to the use of a smaller lung volume) and a similar decrease in Sa with age as that found here. Providing a standardised methodology is used for measurement of K, the present method allows a reasonable estimate of Sa to be obtained during life.     

Changes in glucose turnover parameters during muscular exercise: role of age

In a study of ten young and seven elderly healthy men we have performed an oral glucose tolerance test (75 g) and employed a euglycemic hyperinsulinemic (0.25 mUx kg/min) glucose clamp technique in order to determine insulin sensitivity. This latter experimental protocol consisted of 120 min of euglycemic clamp followed by 60 min in which the clamp and a mild muscular exercise (35% VO(2) (max)) were combined. D-[(3)H]glucose infusion allowed a determination of the glucose turnover parameters. Our results show that in elderly subjects glucose disappearance rate and glucose metabolic clearance rate are significantly lower during both clamp, and clamp + muscular exercise studies. On the contrary, hepatic glucose production was similar under both conditions and was independent of age.     

Changes in serum K+ in healthy and in asthmatic subjects during exercise

Adrenergic mechanisms modulate exercise-induced changes in blood serum K+ concentration ([K+]). Impairment of these same mechanisms may be associated with bronchial hyper-reactivity. If this is accurate, asthmatic subjects should show disturbed K+ regulation during exercise. We measured [K+] and FEV1 in 13 healthy control and in 13 asthmatic subjects pre-exercise, at peak exercise (within 1 min of stopping exercise), and 10 min postexercise. This was done on 2 separate days, one with and one without bronchodilator (BD) pretreatment. Both groups were equally fit, exercising to the same O2 consumption and heart rate. Resting [K+] was normal for both groups (two-day averages were 4.00 +/- 0.07 and 4.09 +/- 0.07 mmol/L, mean +/- SEM, in control and asthmatic subjects, respectively). Without BD pretreatment, at peak exercise, [K+] in control subjects rose by 0.56 +/- 0.08 compared with 0.96 +/- 0.09 in asthmatics (p less than 0.01). After exercise, [K+] returned to baseline (4.12 +/- 0.08) in control subjects but remained elevated in asthmatics (4.60 +/- 0.12, p less than 0.01). Although FEV1 was unchanged in control subjects, in asthmatics it fell after exercise (p less than 0.01). With BD pretreatment: peak exercise [K+] increased by 0.55 +/- 0.09 in control subjects, and by 0.49 +/- 0.01 in asthmatics (p less than 0.01). By 10 min postexercise, it returned to baseline in both groups (4.15 +/- 0.11 for control subjects and 4.32 +/- 0.07 for asthmatics). The asthma group's fall in FEV1 was also abolished. These data indicate that postexercise K+ remains elevated in asthmatics, supporting the suggestion that their adrenergic function is impaired.     

Intrapulmonary gas mixing and the sloping alveolar plateau in COPD patients with macroscopic emphysema.

Chronic obstructive pulmonary disease patients, especially those with emphysema, show steep slopes of the alveolar plateau (S). This study tested the hypothesis that continued gas exchange between poorly and well-ventilated lung units by means of collateral ventilation would contribute to S in these patients. Nine young volunteers, nine older volunteers and 11 patients with macroscopic emphysema performed wash-out tests with helium (He) and sulphur hexafluoride (SF6). S was determined for breaths 1-5 (range 1), and for breaths between 95% and 98% of complete wash-out (range 2). An unequal ventilation index (UVI) was defined as the ratio between the estimated mean alveolar pressure and the end tidal pressure (PET) of each tracer gas, calculated over range 2. Over the same range, a phase III ratio was calculated by dividing PET by the estimated pressure at Fowler dead space. In all groups of subjects, the S for He and SF6 were greater for range 2 than for range 1 (p< or =0.012). In the emphysema patients, the correlations between S and UVI were 0.72 for He (p=0.012) and 0.81 for SF6 (p=0.002), while the mean phase III ratios were 1.7 for He and 2.4 for SF6, much less than their theoretical maxima. It was concluded that in patients collateral ventilation may account for only a small part of the increase in the alveolar plateau slope between ranges 1 and 2, and that this increase was mainly caused by unequal ventilation in combination with sequential emptying of lung units. The degree of sequential emptying, however, was modest compared with its full potential.     

Changes in R wave amplitude during aerobic exercise stress testing in hypertensive adolescents

The change in R wave amplitude during progressive aerobic exercise was studied in hypertensive adolescent boys. A comparable control group consisted of normotensive adolescent boys matched for age, body size and race. Twenty-four normotensive and 22 hypertensive subjects exercised to exhaustion on a treadmill utilizing the Bruce protocol. Blood pressure and heart rate were monitored during exercise and recovery. The change in R wave amplitude in a lead V₅ electrocardiogram was determined at each level of exercise. The normotensive group demonstrated a progressive increase in systolic pressure, heart rate and rate-pressure product (heart rate × systolic pressure) during exercise and a progressive decrease in R wave amplitude with a significant correlation of R wave change versus the cardiac response variable (p < 0.001). Hypertensive subjects manifested a greater increase in systolic pressure, heart rate and rate-pressure product during exercise with no decrease in R wave amplitude until the exercise end point. The difference in R wave response to progressive exercise in the two groups was significant (p < 0.01). A variation in myocardial function in hypertensive adolescents as demonstrated by a difference in R wave response to exercise may reflect a level of peripheral vascular resistance greater than that of normotensive control subjects.     

Changes in transthoracic electrical impedance during submaximal treadmill exercise in patients with ischemic heart disease--A preliminary report.

Twenty normal subjects and 32 patients with ischemic heart disease (IHD) were subjected to submaximal treadmill exercise. The mean transthoracic electrical impedance (TEI) was measured with a tetrapolar lead system and the changes were correlated to the extent of ST depression observed on an on-line digital computer. Six subjects of pre-excitation syndrome with "false" ST depression were also studied. The normal subjects did not show a significant change of TEI during exercise. The patients with IHD showed a steady and significant decrease in TEI, correlating with the extent of ST depression. Recovery was slow after the cessation of exercise. The subjects with false ST changes showed no decrease of TEI. The changes were more profound in subjects who developed anginal pain during the test. These findings are attributed to an increase in the thoracic blood volume and pulmonary extravascular water due to transient left ventricular dysfunction in angina.