1. Progressive exercise and circulatory studies are reporteG on a selecteL group of patients with hypoxaemia and secondary polycythaemia before and after therapeutic decrease of packed cell volume.2. A significant increase in exercise tolerance was demonstrated in a group of seven patients who claimed subjective benefit from the treatment.3. No important circulatory changes were detected at rest after treatment. 4. During steady exercise mean pulmonary artery pressure at any given cardiac output was lower after treatment suggesting a fall in pulmonary vascular resistance. 5. During steady exercise oxygen consumption was increased in five of six patients subjectively improved by the treatment but no consistent changes in arterial lactate concentration or lactate/pyruvate ratio were observed.
Persistent pulmonary hypertension often occurs in infants with meconium aspiration syndrome or asphyxia. There is a subgroup of infants with PPHN in whom myocardiopathy predominates. We reviewed t h e course of 7 infants treated for PPHN who had increased heart size on chest x-ray, and/or an EKG with right ventricular hypertrophy. All patients had documented right-to-left shunting by echocardiogram either through PDA or foramen ovale. Mean B.W. was 3.13 + .49 kg SD (range 2.32 t o 3.74), G.A. was 38.85 5 2.38 weeks SD, Apgars mean of 4.71 2 2.49 SD a t one minute and 6.57 + 2.43 SD a t five minutes. All patients required 790% inspired oxygen concentration, with 6 patients on 100% requiring mechanical ventilation. The following were mean ventilator settings on day one: FiO2 98.57% + 3.77 SD, r a t e 87 + 34.95 SD bpm,
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