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Twenty persons living at an altitude of 2,240 meters were studied in order to examine the relative roles of passive and active factors in the genesis of pulmonary arterial hypertension in obesity (overweight, 75 ± 39 percent). Pulmonary arterial hypertension was present in 80 percent (16) of the patients (mean pulmonary arterial systolic pressure, 45 ± 17 mm Hg). In 95 percent (19) of the 20 patients, resistance to pulmonary flow at the end of diastole was increased (estimated mean pulmonary arteriolar resistance, 210 ± 144 dynes•sec•cm−5; mean pulmonary arterial diastolic-pulmonary wedge pressure gradient 7.86 ± 1.40 mm Hg). The mean arterial oxygen pressure was 50 ± 9 mm Hg, the arterial carbon dioxide tension was 37 ± 6 mm Hg and the arterial pH was 7.42 ± 0.08. Since the pulmonary arterial systolic pressure has been reasonably predicted (r = 0.91; P < 0.001), it would appear that the compliance of the elastic pulmonary arteries in obese patients follows a normal pattern. The behavior of the right ventricular end-diastolic pressure at rest (mean change, 4.6 nun Hg; P < 0.001) and of the pulmonary wedge pressure (mean change, 4.7 mm Hg; P < 0.001) during passive lifting of the legs was indirect evidence of the increase in pulmonary blood volume. The presence of an abnormal resistance to pulmonary blood flow at the end of diastole is suggestive of a decrease in the distention of the pulmonary microcirculation. The pulmonary arterial diastolic-pulmonary wedge pressure gradient and the pulmonary arterial diastolic pressure were related to arterial oxygen unsaturation (r = 0.70; P < 0.05) but not to the concentration of hydrogen ions; thus hypercapnic acidemia appears as a secondary factor in the genesis of pulmonary arterial hypertension at high altitudes. The explanation could be the relative hyperventilation of high altitudes, with a compensatory metabolic alkalosis. The increased pulmonary blood volume and the alveolar hypoxia are the main causes in the pathogenesis of pulmonary arterial hypertension in the grossly obese patient at this altitude.

The experience derived from the administration of isoproterenol in six patients with pulmonary hypertension of unknown etiology (PAH-UE) is presented. The diagnosis was made after exclusion of other known diseases capable of producing hypertension in the pulmonary circuit. Catheterization was performed, and basal cardiopulmonary parameters, mean pulmonary artery pressure (PAP), pulmonary arteriolar resistance (PAR), cardiac index (CI), alveolar-arterial oxygen tension difference P(A-a)O2, and PaO2were investigated. The effect of infusing 3 µg/min of isoproterenol into the pulmonary artery was studied in five cases. Isoproterenol was given sublingually to one patient who had previously received it intravenously; in another case it was given only sublingually. Significant P values (P < .05) as a group were obtained, in relation to heart rate, CI, PAR, and mean PAP after isoproterenol. A favorable effect on the heart and lungs was seen in two cases, maintained for three years with sublingual isoproterenol with a favorable cardiorespiratory effect. Use of isoproterenol in PAH-UE is justified at present in those cases with a favorable cardiopulmonary response while no specific therapy is available.

The experience we describe derives from the short-term administration of isoproterenol in 15 patients with ventricular septal defect (VSD) and severe pulmonary artery hypertension (PAH). For the whole study group, mean pulmonary artery pressure (PAP) was 68.5 ± 2.6 mm Hg, pulmonary vascular resistance (Rp) was 11.6 ± 0.9 U/m2, pulmonary vascular resistance/systemic vascular resistance ratio (Rp/Rs) was 0.9 ± 0.03, and the pulmonary vascular gradient (PAd-PWP) was 45 ± 3.5 mm Hg. Infusions of isoproterenol decreased PAP, Rp, Rp/Rs ratio, and PAd-PWP an average of 10.2 mm Hg, 2.88 U/m2, 0.13, and 6.6 mm Hg, respectively, for the whole group (P < 0.001). On the basis of isoproterenol response, the patients could be divided into two groups: A (n=4) and B (n=11). In group A, the PAP decreased from 61.7 ± 1 to 45 ±4 mm Hg, the Rp from 8.9 ± 0.3 to 4.62 ± 0.5 U/m2, the Rp/Rs from 0.84 ±0.02 to 0.55 ±.05, and the PAd-PWP from 34.5 ± 0.9 to 24 ± 2 mm Hg (mean ± 1 SE). In group B a less significant change in these measurements was observed. Group A patients underwent VSD repair, and the mean average postoperative decrease in PAP was 31 mm Hg (P < 0.001). Our findings suggest that in patients with VSD and severe PAH, in whom surgical treatment is controversial, a trial with isoproterenol should be routinely attempted. If the preceding hemodynamic parameters improve significantly, the VSD repair should be performed.