EFFECT OF MODERATE EXERCISE

Effect of Moderate Exercise on Heart and Breathing Rates



Effect of Moderate Exercise on Heart and Breathing Rates

Introduction

In chronic heart failure (CHF) the consequences of impaired cardiac and respiratory function may be additive, and independently contribute to reduce oxygen saturation and the ability to do physical work. Although previous studies of CHF have shown respiratory dysfunction and the impact controlled breathing has on autonomic control and arterial oxygen saturation (SaO2), the optimum breathing pattern is not known (Marecal, 1981).

Our aim was to establish the optimum breathing rate on SaO2 in patients with CHF and healthy controls, and then assess the effect the optimum rate had on respiratory indices and exercise capacity in CHF patients who were randomly allocated training to this optimum rate.

Methods

We enrolled 50 patients with stable CHF who had had no changes in their signs and symptoms in the 2 weeks before examination and 11 healthy volunteers (controls). The exclusion criteria were pulmonary disease and smoking in the 2 years before the start of the study. None of the controls were smokers and all had normal lung function. The study protocol was approved by the local ethics committee and all individuals gave informed consent to take part (Yeung et al, 1996).

Controls and patients with CHF had simultaneous measurements of heart rate by electrocardiogram, instantaneous lung volume by inductance plethysmography (Respitrace, Ardlsey, NY, USA), non-invasive systolic and diastolic blood pressure (Finapres, Ohmeda, Englewood, CO, USA), and SaO2 (Medlab, Karlsruhe, Germany). We did four breathing recordings: 10 min of spontaneous breathing; 4 min of controlled breathing at 15 breaths per min; 4 min at six breaths per min; and 4 min at three breaths per min. The recording of spontaneous breathing was always done first, and we did not tell patients and controls when recording began. All the recordings of controlled breathing were done in random order. No attempt was made to control the depth of breathing, so that each individual was able to maintain comfortable breathing. We also measured minute ventilation and estimated the ventilation to perfusion inequality (dead-space ventilation to tidal volume ratio) during spontaneous breathing and controlled breathing periods in 15 patients with CHF and in the controls (Pinna et al, 1996).

Analogue signals of heart rate by electrocardiogram, blood pressure, instantaneous lung volume by Respitrace, and SaO2 were simultaneously recorded on computer (mean [SD] values). We used spectral analysis to assess the rate of respiration during spontaneous breathing. Since the respiratory signal by Respitrace estimates tidal volume and minute ventilation in relative terms, values were expressed as % deviation from baseline (spontaneous breathing) for each individual. This limitation could not be avoided because we did not want to affect spontaneous respiration (Levine, 1992).

To test the hypothesis that patients with CHF could have unstable oxygen saturation as a result of irregular breathing, we characterised the respiratory instability by time-varying spectral analysis of respiration which provides an instantaneous description of respiratory rate and amplitude. Respiratory instability was characterised by two indices: the coefficient of variation of ...