[Seasonal variations of blood pressure in normal subjects and patients with chronic disease]. / Variations saisonnières de la pression artérielle chez des sujets normaux et des malades chroniques.

The characteristics and determining factors of seasonal variations of the blood pressure (BP) were studied in 20 normal subjects and 219 chronic stable chronically all patients, most of whom were ambulatory. The BP was measured repetitively over twelve months and measurements in the lying position repeated after one minute of orthostatism were performed in Winter and in Summer. In normal subjects, the BP decreased from June to reach its lowest value in August to return to the Winter values from October. The mean BP of the three Winter months was 130/79 mmHg and the seasonal lowering averages 5 +/- 5/5 +/- 6 mmHg (m +/- SD) (p < 0.01), with marked individual differences. The Summer decrease in BP was observed both lying down (3/4 mmHg) (p = 0.01) and standing (5/6) (p = 0.0001). In the patient group, the Summer decrease in BP was 4/3 mmHg. During the orthostatic measurements, it was 4/4 mmHg lying down and 6/5 mmHg when upright. Symptoms of orthostatic hypotension were reported spontaneously 10 times during the Winter and 21 times during the Summer months (p = 0.04) and occurred in the upright position in 12 patients (6%) in Winter and 25 patients (12%) in Summer (p = 0.025). The Summer decrease was greater in women than in men. Blood pressure lowering drugs increased this effect and the association of several drugs had an additive effect. It increased with age but disappeared after 70-80 years of age. The very elderly patients on antihypertensive therapy showed a marked decrease in BP during the Summer, especially in the upright position. The Summer decrease in BP is important for the management of elderly patients with hypertension or cardiac failure. It may favorize symptoms of orthostatic hypotension and increase the risk of malaise.

[Seasonal variations in arterial pressure in hypertensive patients]. / Variations saisonnières de la pression artérielle chez des patients hypertendus.

Blood pressure (BP) was measured once every month during one year in 80 hypertensive outpatients. An orthostatic test was performed in winter and another during summer. The collective was aged 65 +/- 13 years (m +/- SD) and presented an elevated prevalence of diabetes mellitus, cardiac failure, and coronary, cerebral and arterial insufficiency. Diuretics, betablockers, converting enzyme inhibitors and calcium channel blockers were used by 31 patients as monotherapy and by 49 patients in association. During summer a significantly lower seated BP was found (144.1/79.4 mm Hg vs 150.8/82.9 mm Hg in winter, p < 0.001). One fourth of the patients did not show this diminution. On the basis of the WHO criteria of BP definition, 31% of the patients could be considered hypertensive in winter vs 16% in summer and 28% as normotensive in winter vs 43% in summer (p < 0.05). The summer reduction in BP depended on position. It was less marked in seated position (-5.3/-2.7 mm Hg) than in lying (-6/-5.1 mm Hg) or even in standing position (-10.8/-5.1 mm Hg). The orthostatic test induced a greater immediate fall in systolic BP in summer than in winter (-14.4 vs -9.6 mm Hg, p < 0.001), more orthostatic hypotensive episodes defined as a systolic BP fall of 20 mm Hg or more (34% of patients vs 20% in winter, p = 0.05) and more signs of reduced cerebral perfusion (14% vs 7.5% in winter, NS). Diabetic patients and patients treated by diuretic and vasodilator drugs are particularly exposed to orthostatic hypotension in summer. Betablockers can minimize this risk.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of acid lumen pH on potassium transport in renal cortical collecting tubules.

In order to determine the effect of acid lumen pH on renal tubular potassium transport, cortical collecting tubules were dissected from rabbit kidneys and perfused in vitro. When the pH of the perfusate was lowered from 7.4 to 6.8, potassium secretion into the tubule lumen decreased by an average of 47%. The transepithelial voltage increased from a mean value of -32 mV (lumen negative) at pH 7.4 to -51 mV at PH 6.8. Net sodium absorption from the tubule lumen was essentially unchanged (5% mean decrease). Transepithelial voltage and potassium secretion returned to control values when the pH of the perfusate was raised to 7.4. Alterations in pH of the bath had no comparable effect on the transepithelial voltage, whether the bath pH was increased or decreased. We conclude that a decrease in the pH of the tubule fluid of itself inhibits active potassium secretion in this tubule segment, providing an additional explanation for the decrease in potassium excretion found in acidosis. The negative voltage (presumably caused by sodium absorption out of the lumen) is increased under these conditions, possibly because of reduction of a smaller counterbalancing positive voltage caused by potassium secretion into the lumen.