L. Bernardi et al., EFFECT OF BREATHING RATE ON OXYGEN-SATURATION AND EXERCISE PERFORMANCE IN CHRONIC HEART-FAILURE, Lancet, 351(9112), 1998, pp. 1308-1311
Background In chronic heart failure (CHF), impaired pulmonary function
can independently contribute to oxygen desaturation and reduced physi
cal activity. We investigated the effect of breathing rate on oxygen s
aturation and other respiratory indices. Methods Arterial oxygen satur
ation (SaO(2)) and respiratory indices were recorded during spontaneou
s breathing (baseline) and during controlled breathing at 15, six, and
three breaths per min in 50 patients with CHF and in 11 healthy volun
teers (controls). 15 patients with CHF were randomly allocated 1 month
of respiratory training to decrease their respiratory rate to six bre
aths per min. Respiratory indices were recorded before training, at th
e end of training, and 1 month after training. Findings During spontan
eous breathing, mean SaO(2) was lower in CHF patients than in controls
(91.4% [SD 0.4] vs 95.4% [0.2], p<0.001). Controlled breathing increa
sed SaO(2) at all breathing rates in patients with CHF. Compared with
baseline, minute ventilation increased at 15 breaths per min (+45.9% [
9.8], p<0.01), did not change at six breaths per min, and decreased at
three breaths per min (-40.3% [4.8], p<0.001). In the nine CHF patien
ts who had 1 month of respiratory training, resting SaO(2) increased f
rom 92.5% (0.3) at baseline to 93.2% (0.4) (p<0.05), their breathing r
ate per min decreased from 13.4 (1.5) to 7.6 (1.9) (p<0.001), peak oxy
gen consumption increased from 1157 (83) to 1368 (110) L/min (p<0.05),
exercise time increased from 583 (29) to 615 (23) min/s (p<0.05), and
perception of dyspnoea reduced from a score of 19.0 (0.4) to 17.3 (0.
9) on the Borg scale (p<0.05). There were no changes in the respirator
y indices in the patients who did not have respiratory training. Inter
pretation Slowing respiratory rate reduces dyspnoea and improves both
resting pulmonary gas exchange and exercise performance in patients wi
th CHF.