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Biomedical subjects

A Melcher

Publications and source records attributed to A Melcher.

At least 55 records · Page 3Linked to original sources
PubMed1978

Exercise energy expenditure in extreme obesity: influence of ergometry type and weight loss.

Bicycle and treadmill exercise tests including oxygen uptake (VO2) and heart rate (HR) determination were carried out on a total of thirty patients with obesity, seventeen of whom were reinvestigated after weight loss. During both types of work VO2 for a given load was higher when compared to healthy controls. The increase of VO2 was more marked when cycling was performed in sitting position than in supine. The mechanical efficiency of sitting bicycle exercise averaged 17.8% and was negatively related to the percentage overweight; the slope of the VO2/load regression line was slightly less in comparison to the controls, while no such difference was found during treadmill walking. After weight reduction the VO2/load regression line was skifted downwards, the slopes being unchanged, thus the mechanical efficiency improved. This study not only confirms the observation of a low mechanical efficiency of obese subjects but also demonstrates that the change is quantitatively related to the overweight. The lowered efficiency was caused by body mechanical factors and there was no support for an abnormal muscular efficiency. Exercise tests should be combined with VO2 determination, if used to assess the circulatory capacity of obese subjects.

Adult↗
PubMed1976

Effects of cedilanid-D in combination with metoprolol on exercise tolerance and systolic time intervals in angina pectoris.

The interaction between cedilanid-D and metoprolol, a selective beta receptor blocking agent, on exercise tolerance and systolic intervals was studied in 15 patients with angina pectoris. The patients had been treated with metoprolol for several months in a dose of 50 mg, three times daily (one patient received 25 mg three times daily). Each patient participated in two studies separated by at least 1 week. After arriving at the laboratory each received 50 mg of metoprolol orally; thereafter, either cedilanid-D or placebo was infused intravenously in a double-blind study performed in randomized order. When the effect of the drugs was maximal, the systolic intervals and the heart volume were recorded at rest, and the exercise tolerance was tested with a bicycle ergometer. The mean maximal value of plasma concentrations of metoprolol assessed during the study was about 50 ng/ml but the variation among subjects was great (20 to 187 ng/ml). After administration of cedilanid-D there was a shortening of the pre-ejection period and left ventricular ejection time compared with results after placebo; the reduction was similar to that found after administration of cedilanid-D without beta blocking drugs. The total heart volume decreased by an average of 55 ml, but the individual variation was great. The patients' average work capacity, expressed as total work, was not altered by cedilanid-D when compared with results after placebo. No relation was found between initial heart size and the effect of cedilanid-D on capacity for physical work. It therefore appears that there is no indication for the routine use of digitalis during beta blocking therapy in patients with angina pectoris who do not have cardiac failure.

Adrenergic beta-Antagonists↗
PubMed1976

Sinus arrhythmia in man: influence of tidal volume and oesophageal pressure.

The effect of tidal volume (VT) and of the intrathoracic pressure (Poes) on the respiratory sinus arrhythmia (RSA) was studied in healthy subjects. They breathed into a spirometer with a VT of 1, 1.5, and 2 1, at a standardized, slow respiratory rate, 6-min-1 (A). Poes was varied by (B) adding a negative inspiratory pressure (NIP) of 5 cm of water and by (C) intermittent positive pressure ventilation (IPPV) at identical VT and respiratory frequency. In separate study (D), intermittent negative pressure ventilation (INPV) was induced by applying negative pressure on the thorax. In A, increasing VT provoked an augmented RSA by a more marked tachycardia as well as bradycardia. On increasing the amplitude of Poes in B, RSA was somewhat more marked due to a lower minimum heart rate. Whem comparing respiratory cycles that had similar Poes but a different VT, the larger VT caused a slight increase in the RSA amplitude due to a more marked deceleration of the heart rate. IPPV almost abolished RSA, whereas INPV did not reduce the arrhythmia. It is concluded that pulmonary stretch reflexes to a minor extent contribute to RSA, whereas the hypothesis of a central nervous origin does not gain support. Cardiovascular reflexes remain the main possible cause of RSA.

Adult↗
PubMed1976

Respiratory sinus arrhythmia in man: relation to cardiovascular pressures.

The relationship of respiratory sinus arrhythmia (RSA) to the accompanying oscillations of cardiovascular pressure has been studied in five healthy subjects. Tidal volume (VT) of 1.0, 1.5, and 2.0 1 at the breathing rate of 6 c-min-1 were used as reference. With identical VT oesophageal pressure was varied by negative inspiratory pressure (NIP) and intermittent positive-pressure ventilation (IPPV). Compared with control, NIP with 1.01 significantly increased RSA, the oscillations of brachial artery pressures (PBA), and the net filling pressures of the ventricles. IPPV did not significantly change the variations of PBA but reduced RSA and the respiratory variations of the right ventricular end-diastolic net pressure. During control breathing and with NIP the acceleration of heart rate during inspiration was associated with rising PBA and rising net filling pressures of both ventricles. The results indicate that RSA may be elicited by cardiovascular reflexes due to changes in venous filling of the heart rather than by the variations in systemic arterial pressure.

Adult↗
PubMed1976

Respiratory sinus arrhythmia in man: relation to right ventricular output.

The respiratory effects on heart rate (HR), right ventricular stroke volume (SV RV) and the pulmonary arterial flow (PAF) have been studied beat-by-beat in seven conscious, healthy subjects. Tidal volumes (VT) of 1.0 and 2.0 liters at a breathing rate of 6 c x min-1 were used as controls. With identical VT and respiratory rate intrathoracic was affected by (A) negative inspiratory pressure (NIP) of 5 cm of water and (B) with intermittent positive pressure ventilation (IPPV). In the control experiments all subjects exhibited an inspiratory increase in HR (respiratory sinus arrhythmia) as well as in SV RV. With VT of 1.0 liter, NIP augmented the inspiratory increase in SV RV and the respiratory oscillations of PAF. IPPV decreased SV RV and HR during inspiration. It is concluded that NIP and IPPV affect the SV RV and the right heart blood flow. The similar effects on HR and SV RV suggest a causal relationship which might be explained by heart rate regulating reflexes from the heart.

Adult↗
PubMed1976

Respiratory sinus arrhythmia in man: effects of carotid sinus baroreceptor stimulation.

1. The role played by the carotid sinus baroreflex in the genesis of the respiratory sinus arrhythmia (RSA) was studied in nine healthy subjects. The carotid sinus baroreceptors were stimulated by the application of subatmospheric to the neck. 2. Reducing the normal respiratory arterial pressure oscillations and changing the phase between the pressure oscillations and the respiration did not affect the RSA. 3. Stimuli applied during expiration only, augmented the arrhythmia, while inspiratory stimulation was without any effect. 4. It is suggested that changes in the arterial baroreflex set point and/or gain during the respiratory cycle contribute to RSA in man.

Adult↗
PubMed1976

Respiratory sinus arrhythmia in man: relation to cardiovascular pressures.

The relationship of repiratory sinus arrhythmia (RSA) to the accompanying oscillations of cardiovascular pressures has been studied in five healthy subjects. Tidal volumes (VT) of 1.0, 1.5, and 2.0 1 at a breathing rate of 6 c-min(-1) were used as reference. With identical VT, oesophageal pressure was varied by negative inspiratory pressure (NIP) and intermittent positive-pressure ventilation (IPPV). Compared with control, NIP with 1.01 significantly increased RSA, the oscillations of brachial artery pressures (PBA), and the net filling pressures of the ventricles. IPPV did not significantly change the variations of PBA but reduced RSA and the repiratory variations of the right ventricular end-diastolic net pressure. During control breathing and with NIP the acceleration of heart rate during inspiration was associated with rising PBA and rising net filling pressures of both ventricles. The results indicate that RSA may be elicited by cardiovascular reflexes due to changes in venous filling of the heart rather than by the variations in systemic arterial pressure.

Adult↗
PubMed1976

Respiratory sinus arrhythmia in man: relation to right ventricular output.

The respiratory effects on heart rate (HR), right ventricular stroke volume (SVRV), and the pulmonary arterial flow (PAF) have been studied beat-by-beat in 7 conscious, healthy subjects. Tidal volumes (VT) of 1.0 and 2.0 liters at a breathing rate of 6 cXmin-1 were used as controls. With identical VT and respiratory rate intrathoracic pressure was affected by (A) negative inspiratory pressure (NIP) of 5 cm of water and (B) with intermittent positive pressure ventilation (IPPV). In the control experiments all subjects exhibited an inspiratory increase in HR (respiratory sinus arrhythmia) as well as in SVRV. With VT of 1.0 liter, NIP augmented the inspiratory increase in SVRV and the respiratory oscillations of PAF. IPPV decreased SVRV and HR during inspiration. It is concluded that NIP and IPPV affect the SVRV and the right heart blood flow. The similar effects on HR and SVRV suggest a relationship which might be explained by heart-rate-regulating reflexes from the heart.

Adult↗
PubMed1975

Exercise tolerance in patients with angina pectoris after pentaerythritol trinitrate and alprenolol studied by two different methods.

Exercise tolerance has been studied by two different methods, heart-rate-controlled exercise and stepwise increased load, in 12 patients with angina pectoris. The response to a beta-adrenergic blocking agent, alprenolol, and an alkyl nitrate derivative, pentaerythritol trinitrate (PETRIN) was studied by the two methods after double-blind administration of the drugs. Rating scales were used to quantitate the degree of dyspnoea, angina pectoris and tiredness in the legs. After PETRIN both methods showed significant increases in exercise tolerance (19 and 21 per cent). The heart-rate-controlled test showed a significant increase (33%) after alprenolol, but the change was not significant by the other method. In the patients studied, heart-rate-controlled exercise discriminated between active drug and placebo better than the stepwise increased load test, what might have been due to more optimal matching of the loads obtained in the heart-rate-controlled test. Indications are given about how to design an exercise study in patients with angina pectoris.

Aged↗
PubMed1975

Circulatory and respiratory adaptation in man to acute withdrawal and reinfusion of blood.

In eight healthy men 950 g of blood (12.2 17.6% of the blood volume) was withdrawn and reinfused after about half an hour. Respiration and circulation were studied by analyses of expiratory gas, blood gases and data from right heart catheterization. On hemorrhage oxygen uptake and cardiac output decreased by 10 and 28%, repectively; both varied indirectly with the blood loss. The pressures in the right ventricle, pulmonary and systemic arteries fell without relation to the cardiac output. Mean heart rate did not change significantly, but a moderate positive covariation (P less than 0.05) between heart rate and arterial blood pressure was found during bleeding. This result was confirmed by the relative bradycardia noted in the period prior to reinfusion. On refilling of the bood the oxygen uptake and the pulmonary arterial pressures increased above the initial value. The heart rate varied directly with the arterial pressure also during reinfusion. The observations demonstrate a depression of the metabolism and circulation on moderate hemorrhage. Part of these effects is tentatively referred to a lowered set point of the arterial baroreflexes.

Adaptation, Physiological↗
PubMed1975

Sinus arrhythmia in man: influence of tidal volume and oesophageal pressure.

The effect of tidal volume (VT) and of the intrathoracic pressure (Poes) on the respiratory sinus arrhythmia (RSA) was studied in healthy subjects. They breathed into a spirometer with a VT of 1, 1.5, and 2 1, at a standardized, slow respiratory rate, 6-min-1 (A). Poes was varied by (B) adding a negative inspiratory pressure (NIP) of 5 cm of water and by (C) intermittent positive pressure ventilation (IPPV) at identical VT and respiratory frequency. In a separate study (D), intermittent negative pressure ventilation (INPV) was induced by applying negative pressure on the thorax. In A, increasing VT provoked an augmented RSA by a more marked tachycardia as well as bradycardia. On increasing the amplitude of Poes in B, RSA was somewhat more marked due to a lower minimum heart rate. When comparing respiratory cycles that had similar Poes but a different VT, the larger VT caused a slight increase in the RSA amplitude due to a more marked deceleration of the heart rate. IPPV almost abolished RSA, whereas INPV did not reduce the arrhythmia. It is concluded that pulmonary stretch reflexes to a minor extent contribute to RSA, whereas the hypothesis of a central nervous origin does not gain support. Cardiovascular reflexes remain the main possible cause of RSA.

Adult↗
PubMed1973

Cardiorespiratory and metabolic costs of continuous and intermittent exercise in man.

1. Cardiorespiratory and metabolic responses to paired patterns of continuous and intermittent exercise with the same average power output were studied in eight men. Heart rate, ventilation and pulmonary gas exchange were measured during the different patterns of exercise performed on a cycle ergometer. The recovery oxygen volume was measured over 30 min of loadless pedalling. Needle biopsy samples of the vastus lateralis muscle were taken before, during and after completion of the exercise for measurement of muscle metabolites.2. Heart rate, ventilation, oxygen intake, respiratory exchange ratio, and blood lactate concentration were generally higher with intermittent compared with continuous exercise as were the accumulated totals for heart beats, ventilation and oxygen intake. Muscle biopsy samples tended to have higher lactate and lower phosphocreatine contents in intermittent exercise. The lactate concentration in muscle and blood water was the same during loadless pedalling before exercise but was significantly higher in muscle than blood during exercise. This concentration gradient was larger in intermittent than in continuous exercise.3. Work efficiency, calculated from the total oxygen cost of work in excess of a loadless pedalling control, was significantly lower in intermittent exercise. The explanation is thought to be connected with the observation that when the work was performed at a high rate in short bursts a large part of the oxidative recovery took place after the contraction during the rest periods, whereas in the low intensity continuous exercise the oxygen was mainly utilized while the work was being performed. This indicates that for part of the time in the intermittent exercise the muscle was working under anaerobic conditions. Although the possibility exists that the efficiency of resynthesis of phosphagen may be reduced in this form of activity, it is more likely that the result described is due to the greater amount of lactate formed in the intermittent exercise.

Adenosine Triphosphate↗