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Biomedical subjects

B J Whipp

Publications and source records attributed to B J Whipp.

At least 163 records · Page 9Linked to original sources
PubMed1978

Ventilatory and gas exchange responses to cycling with sinusoidally varying pedal rate.

To investigate factors controlling ventilation under conditions where the applied work load remains constant, but where hypothesized proprioceptive influences would be expected to vary, five subjects exercised at a constant work rate of 50 W on a cycle ergometer at pedaling rates which varied sinusoidally between 40 and 80 rpm. Each subject exercised continuously for 30 min at each of five sinusoidal periods. Minute ventilation (VE), carbon dioxide output (VCO2), oxygen uptake (VO2), and heart rate were computed breath-by-breath and amplitude and phase relations were extracted. We observed small fluctuations in VCO2 and VO2 engendered by varying metabolic requirements of moving the legs at varying rates. VE fluctuations were closely in phase with VCO2 and the amplitudes of the fluctuations were highly significantly correlated (r = 0.83, P less than 0.001); consequently end-tidal carbon dioxide tension fluctuations were small. Variation of pedaling rate, therefore, did not produce a ventilatory response independent of the effect of VCO2. The ventilatory responses to these forcings are inconsistent with an appreciable role for neurally mediated influences from the exercising limbs and provide further evidence that the exercise hyperpnea is linked to CO2 flow to the central circulation.

Adult↗
PubMed1978

Control of ventilation during intravenous CO2 loading in the awake dog.

The ventilatory response to venous CO2 loading and its effect on arterial CO2 tension was determined in five awake dogs. Blood, 200-500 ml/min, was diverted from a catheter in the right common carotid artery through a membrane gas exchanger and returned to the right jugular vein. CO2 loading was accomplished by changing the gas ventilating the gas exchanger from a mixture of 5% CO2 in air to 100% CO2. The ventilatory responses to this procedure were compared with those resulting from increased inspired CO2 concentrations (during which ventilation of the gas exchanger with the air and 5% CO2 mixture continued). The ventilatory response to each form of CO2 loading was computed as deltaVE/deltaPaco9. The mean ventilatory response to airway CO2 loading was 1.61 1/min per Torr PaCO2. The mean response for the venous CO2 loading was significantly higher and not significantly different from "infinite" CO2 sensitivity (i.e., isocapnic response). The results provide further evidence for a CO2-linked hyperpnea, not mediated by significant changes in mean arterial PCO2.

Animals↗
PubMed1978

Effect of hypercapnia on hypoxic ventilatory drive in carotid body-resected man.

Steplike end-tidal hypoxic drives (PETCO2 = 53 Torr) lasting for 5 min were generated in a group of normal subjects and a group of carotid body-resected subjects when end-tidal CO2 was maintained constant under eucapnic (PETCO2 = 39 Torr) and hypercapnic (PETCO2 = 49 Torr) conditions. The hypoxic ventilatory response of the normal subjects was prompt and significant in eucapnia and was enhanced in the hypercapnic state, evidencing CO2-O2 interaction. In contrast, the carotid body-resected subjects did not respond to eucapnic hypoxia but did demonstrate a small but significant ventilatory response to hypoxia against the hypercapnic background. This suggests that the aortic bodies in man may contribute a small component of the hypoxic ventilatory drive under hypercapnic conditions, although the possibility of neuromalike ending regeneration cannot be excluded.

Adult↗
PubMed1977

Some respiratory and metabolic effects of exercise in moderately obese men.

The effects of varying levels of exercise on oxygen uptake, CO2 production, blood pressure, arterial blood gasses, and arterial concentrations of glucose, insulin, and growth hormone were examined in ten normal weight and ten moderately overweight young men. At comparable external work loads with a bicycle ergometer, the lean men required less oxygen than the obese men. When oxygen uptakes were matched during exercise on a treadmill, the lean men were walking on a steeper grade or at a higher rate than the obese men. The efficiency of exercise as assessed by the relation between oxygen uptake and work did not differ between the two groups. Blood pressure rose more in the obese during exercise than in the lean. The fall in lactate and rise in bicarbonate was of greater magnitude during cycle ergometry than during treadmill exercise. Obese and lean men, however, showed similar changes. With each level of exercise, there was a fall in arterial insulin levels, but the concentrations in the blood of overweight men always remained significantly above that of the normal men. Growth hormones tended to be higher in the normal weight men, but the differences were usually not significant, and there was no significant rise with exercise in either group until the highest levels of work were achieved. Glucose concentrations tended to be higher in the obese men, but fell to constant levels in both groups during exercise. Blood pressure rose to a greater extent in the overweight men during exercise.

Adolescent↗
PubMed1977

Very small, very short-latency changes in human breathing induced by step changes of alveolar gas composition.

1. Three healthy young males were maintained for sessions of about 1 hr in a state of mild asphyxia (PA,O2 approximately 55, PA,CO2 approximately 45 torr), i.e. with moderately strong drives from both arterial and intracranial chemoreceptors. Tidal volume (VT), breath duration (TT) and duration of inspiration (TI) were recorded, and ventilation (VE) and duration of expiration (TE) were derived breath by breath. 2. The arterial chemoreceptor component of the drive was briefly and abruptly reduced, perhaps silenced, by three separate procedures: the inspiratory pathway was connected for two breaths to a second gas supply line containing, B, hypoxia with Pi,CO2 zero (removal of hypercapnia with maintained hypoxia); C, pure oxygen (removal of asphyxia); and D, oxygen with 40 torr added PCO2 (removal of hypoxia with maintained hypercapnia). In controls, A, the second inspiratory line contained the maintenance mixture so that the switch involved no change of inspiratory gas composition. Each type of test was repeated twenty-four times on each subject. 3. Responses attributable to silencing of arterial chemoreceptors (i.e. with 1 1/2--3 breath latencies about equal to the lung-to-ear circulation time) are reported elsewhere. 4. Very small responses, occurring only half a respiratory cycle after first inhalation of the test mixture, were detected by pooling all responses of each kind from all subjects. When hypoxia was withdrawn, with (C) or without (D) simultaneous withdrawal of hypercapnia, VT and VE were reduced by 3 and 2% respectively, probably because gas mixtures containing high oxygen concentrations are appreciably more viscous than hypoxic mixtures and so require more effort to breathe in and out. When hypercapnia was withdrawn with (C) or without (B) simultaneous withdrawal of hypoxia, TE was significantly lengthened (mean, + 65 +/- 18 msec), 5. The change of TE was discussed in relation to known effects of CO2 on airway receptors in the dog.

Carbon Dioxide↗
PubMed1977

Ventilatory and gas exchange dynamics in response to sinusoidal work.

The dynamic relationships between ventilation and gas exchange variables during exercise were determined utilizing frequency analysis techniques. Five subjects exercised on a cycle ergometer for 30 min at work rates which fluctuated sinusoidally between 25 W and 80% of the anaerobic threshold at sinusoidal periods of 0.7, 1,2,4,6, and 10 min. VE, VCO2, VO2, and HR were computed and displayed breath-by-breath. From these and steady-state response data, digital computer routines extracted amplitude and phase relations between each variable and the perturbing work load. These response characteristics were well described by first-order linear dynamics with time constants for VE, VCO2, VO2, and HR averaging 1.4, 1.2, 0.8, and 0.8 min, respectively. The time constants of VE and VCO2 were strongly correlated among subjects (r = 0.97). Further, there was no evidence that neural afferents from the exercising limbs induced fast components in the ventilatory response to these forcings. These results are consistent with the hypothesis that exercise hyperpnea is linked to metabolism via carbon dioxide production.

Adult↗
PubMed1977

Kinetics of gas exchange and ventilation in transitions from rest or prior exercise.

Seven normal subjects each performed three transitions to a subanaerobic threshold work rate on a cycle ergometer: 1) from rest, 2) from a low work rate (both at 60 rpm), and 3) from a low work rate at 40 rpm to the high work rate at 80 rpm. Oxygen uptake (VO2), carbon dioxide output (VCO2), and ventilation (VE) were computed breath-by-breath and response kinetics extracted. The mean half-times of VO2, VCO2, and VE were 32, 44, and 49 s, respectively, and were not appreciably affected by the prior exercise or by variation of pedal rate. The kinetics of VE was highly correlated with VCO2 (r = 0.94), with VCO2 leading VE, providing further description of the relation of the exercise hyperpnea to CO2 flow to the lungs.

Adolescent↗
PubMed1976

Ventilatory responses to the metabolic acidosis of treadmill and cycle ergometry.

Ventilation and acid-base responses were studied at comparable levels of O2 uptake during cycle ergometer and treadmill exercise, to determine the extent to which the type of exercise affects these responses. Twenty male subjects performed 50-, 100-, and 150-W cycle ergometer exercise and three work rates of similar O2 uptake on a treadmill. At comparable oxygen uptakes, arterial lactate and VE were higher and arterial pH and bicarbonate were lower for cycle ergometer than treadmill exercise. These differences could be accounted for by the greater degree of metabolic acidosis during cycle ergometer work. The increment in VE over that predicted (from an extrapolation of the linear relationship of the VE-VO2 relationship for low work rates) was linearly related to the decrease in arterial bicarbonate; VE was increased by approximately 4 1/min for each meq/1 of bicarbonate decrease for both treadmill and cycle ergometry.

Acid-Base Equilibrium↗
PubMed1976

Role of the carotid bodies in the heart rate response to breath holding in man.

To investigate the role of the carotid bodies in regulating the bradycardia of breath holding in man, we studied heart rate (HR) responses to prolonged breath holding (BH) in five asymptomatic asthmatic patients whose carotid bodies had been resected (CBR). Seven normal subjects served as controls. BH experiments were randomly initiated with single breaths of 100%, 21%, or 12% 92. During BH with 21% O2, normal subjects displayed the typical bradycardia; this response, however, was attenuated with the other O2 concentrations. In contrast, the CBR subjects manifested BH tachycardia which was inversely proportional to the O2 tension. HR increased in be CBR group by 5%, 31%, and 45% during BH with 100%, 21%, and 12% O2, respectively. These results demonstrate that the bradycardia of BH in normal man is under the influence of the carotid bodies. During BH and in the absence of carotid bodies, an O2 tension-dependent tachycardia is unveiled.

Adult↗
PubMed1976

Effect of beta-adrenergic blockade during exercise on ventilation and gas exchange.

The ventilatory effects of beta-adrenergic blockade during steady-state exercise were studied in eight normal subjects using intravenous propranolol hydrochloride (0.2 mg/kg). Heart rate decreased in all subjects by an average of 17%. Coincident with the phase of decreasing heart rate was a significant decrease in both minute ventilation (VE) and CO2 output (VCO2), averaging 9.6 and 9.2%, respectively. Both functions returned to prepropranolol levels after heart rate had reached its reduced steady-state value. The change in VE was significantly correlated with the change in VCO2 (r = 0.85, P less than 0.005), and was associated with negligible changes in endtidal CO2 tensions and ventilatory equivalents for CO2. We interpret these studies as showing that the transient isocapnic hypopnea concomitant with an acute reduction in cardiac output was secondary to a transient decrease in CO2 flux (cardiac output x mixed venous CO2 content). This decrease in VE appears to be induced by the acute decrease in cardiac output ("cardiodynamic hypopnea"), in fashion similar to the previously described cardiodynamic hyperpnea.

Adolescent↗
PubMed1975

A sinusoidal load generator for use in cycle ergometry.

We have modified an electromagnetically braked cycle ergometer to provide a sinusoidally varying work load. This was accomplished by applying a low-frequency sinusoidal voltage at the inputs of the electromagnets using a sinusoidal potentiometer, whose shaft was driven by a variable-speed motor, and a voltage-programmable power supply to amplify the signal. The frequency range is currently 0.0017-0.3 Hz. This technique for sinusoidal work loads allow the period, amplitude, and mean position to be easily changed from a console, even during a test if required.

Electronics↗