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Biomedical subjects

J P Nicholson

Publications and source records attributed to J P Nicholson.

At least 19 recordsLinked to original sources
PubMed2003

The anaesthetic management of a patient with a reninoma.

We report on the anaesthetic management of a 28-year-old woman presenting for excision of a reninoma. This is a very rare tumour of the juxtaglomerular cells of the kidney, which can be cured immediately by surgery. Previous reports have failed to record the presence or absence of peri-operative cardiovascular lability. We have shown that blood pressure, cardiac index (CI) and systemic vascular resistance (SVRI) were remarkably stable in our patient throughout surgery, even during manipulation of the tumour. Isolation of the tumour was associated with a 23% reduction in SVRI, and a similar decrease in blood pressure. The cardiovascular lability associated with the removal of catecholamine-secreting tumours was not seen in this case.

Adenocarcinoma↗
PubMed2001

Relation of cellular potassium to other mineral ions in hypertension and diabetes.

To investigate the role of intracellular potassium (K(i))and other ions in hypertension and diabetes, we utilized (39)K-, (23)Na-, (31)P-, and (19)F-nuclear magnetic resonance (NMR) spectroscopy to measure K(i), intracellular sodium (Na(i)), intracellular free magnesium (Mg(i)), and cytosolic free calcium (Ca(i)), respectively, in red blood cells of fasting normotensive nondiabetic control subjects (n=10), untreated (n=13) and treated (n=14) essential hypertensive subjects, and diabetic subjects (n=5). In 12 subjects (6 hypertensive and 6 normotensive controls), ions were also measured before and after the acute infusion of 1 L of normal saline. Compared with those in controls (K(i)=148+/-2.0 mmol/L), K(i) levels were significantly lower in hypertensive (132.2+/-2.9 mmol/L, sig=0.05) and in type 2 diabetic subjects (121.2+/-6.8 mmol/L, sig=0.05). K(i) was higher in treated hypertensives than in untreated hypertensives (139+/-3.1 mmol/L, sig=0.05) but was still lower than in normals. Although no significant relation was observed between basal K(i) and Na(i) values, saline infusion elevated Na(i) (P<0.01) and reciprocally suppressed K(i) levels (142+/-2.4 to 131+/-2.2 mmol/L, P<0.01). K(i) was strongly and inversely related to Ca(i) (r=-0.846, P<0.001), and was directly related to Mg(i) (r=0.664, P<0.001). We conclude that (1) K(i) depletion is a common feature of essential hypertension and type 2 diabetes, (2) treatment of hypertension at least partially restores K(i) levels toward normal, and (3) fasting steady-state K(i) levels are closely linked to Ca(i) and Mg(i) homeostasis. Altogether, these results emphasize the similar and coordinate nature of ionic defects in diabetes and hypertension and suggest that their interpretation requires an understanding of their interaction.

Aged↗
PubMed1998

Serum albumin and colloid osmotic pressure in survivors and nonsurvivors of prolonged critical illness.

We retrospectively compared the changes in serum albumin concentration and colloid osmotic pressure between survivors and nonsurvivors of prolonged (> or = 7 days) critical illness over a 2-year period from 1 July 1995. All patients had serum albumin measured daily, and colloid osmotic pressure measured 5 days a week, throughout their ICU admission. They received crystalloid and colloid infusions as well as parenteral or enteral feeding. Infusions of albumin were not used to treat hypoalbuminaemia. One hundred and forty-five patients were included, 66 nonsurvivors and 79 survivors. Nonsurvivors were significantly older than survivors [mean (95% CI): 58 (3.8) and 49 (4.1) years, respectively] and had a greater risk of death [mean (95% CI): 0.44 (0.06) and 0.28 (0.05); p < 0.05]. There was no significant difference in gender, APACHE II score [mean (95% CI): 22 (2.7) (nonsurvivors); 18 (2.3) (survivors)] or length of stay [median (interquartile range): 14 (9-27) days (nonsurvivors); 15 (9-26) days (survivors)]. There was no difference between the two groups in the absolute minimum serum albumin concentrations reached, the time to reach that minimum or the minimum in the first 7 days. However, nonsurvivors had a significantly lower mean serum albumin concentration: [mean (95% CI): 15.7 (5.1) g.l-1 compared with 18.3 (4.6) g.l-1 in survivors; p < 0.05]. They also had a lower recovery mean (the weighted mean after the minimum value): [mean (95% CI): 13.3 (5.1) g.l-1 (nonsurvivors) and 18.6 (5.3) g.l-1 (survivors); p < 0.01]. Analysis of colloid osmotic pressure results showed no difference between the groups in mean, minimum or recovery mean. Regression analysis of mean colloid osmotic pressure and albumin revealed that albumin only contributed 17% of the colloid osmotic pressure in these patients. The similar decrease in albumin in nonsurvivors and survivors may reflect the acute inflammatory response and/or haemodilution. However, survivors showed an ability to increase serum albumin concentrations, possibly owing to resumption of synthesis. The colloid osmotic pressure varied little between or within either group of patients, possibly because of the use of artificial colloids. There was no relationship between death and colloid osmotic pressure.

Adult↗
PubMed1992

Massive theophylline dosing in a heavy smoker receiving both phenytoin and phenobarbital.

OBJECTIVE: To report unusually high theophylline dosing requirements in a smoker receiving concomitant therapy with phenytoin and phenobarbital. DESIGN: Single case report. SETTING: 517-bed, university teaching hospital. PATIENT: 29-year-old woman with newly diagnosed asthma, heavy smoking history, and a seizure disorder. RESULTS: The additive influence of smoking, phenytoin, and phenobarbital greatly increased the theophylline dosing requirements. Doses of up to 4 g/d (59 mg/kg/d) were required to achieve adequate symptomatic relief of her asthma as well as to provide therapeutic serum theophylline concentrations. CONCLUSIONS: Multiple polymorphisms may additively influence theophylline metabolism and exceptionally large theophylline doses may be required in some patients who smoke and are comedicated with phenytoin and phenobarbital.

Adult↗
PubMed1991

The pressor effect of sodium-volume expansion is calcium mediated.

To investigate the calcium dependence of salt-induced hypertension we concurrently measured blood pressure and serum ionized calcium in conscious normotensive female dogs undergoing five infusions: 1) sodium chloride (0.9%) 2) calcium chloride (10 mg/kg), 3) combined sodium chloride and calcium chloride, 4) nicardipine (1 micrograms/kg/min), and 5) combined sodium chloride and calcium chloride in the presence of nicardipine. While saline and calcium chloride infusions individually did not affect blood pressure, saline combined with calcium chloride significantly and consistently raised mean arterial pressure (MAP) (delta MAP = 7 +/- 2 mm Hg, P less than .001 v baseline). Serum ionized calcium (Caio) levels increased within the normal range with the infusion of calcium alone (1.32 +/- 0.03 to 1.48 +/- 0.01 mmol/L, P less than .005). Extracellular Caio rose less with the combined NaCl-CaCl2 infusion (delta Caio 0.10 +/- 0.01 v 0.16 +/- 0.02 mmol/L, P less than .02). The difference in calcium elevations could not be attributed to volume expansion alone, since saline infusion itself did not affect serum ionized calcium (1.32 +/- 0.3 to 1.31 +/- 0.01 mmol/L, P = NS). Furthermore, nicardipine prevented the pressor effect of the combined saline-calcium infusion. (delta MAP = -2 +/- 3 v 7 +/- 2 mm Hg, P less than .001), and restored the rise in extracellular Caio to that seen with the nonpressor calcium infusion (delta Caio 0.15 +/- 0.01 mmol/L v 0.16 +/- 0.02 mmol/L, P = NS). Altogether, these data demonstrate that the rise in blood pressure and ionized calcium following an acute infusion of sodium and calcium chloride are interdependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

The effects of calcium channel blockade on blood pressure and calcium metabolism.

To study the relation of calcium channel blockade to calcium metabolism, we measured serum ionized calcium (Ca++i0), magnesium (Mg), calcitonin (CT), and 1,25-dihydroxyvitamin D (1,25-D) before and after short-term therapy with verapamil 120 mg three times daily in essential hypertensive subjects on low (10 mEq) and high (200 mEq) dietary sodium intakes. Salt-sensitive compared with salt-insensitive subjects on high v low dietary salt intake had lower Ca++i0 (P less than .05), higher 1,25-D (P less than .02), and a greater hypertensive responsive to verapamil (% delta DBP = 17.7 v -8.2, P less than .05). The % delta DBP was related to the initial CT (r = 0.68, P less than .05), initial 1,25-D (R = -0.89, P less than .01), and to the drug-induced % delta 1,25 D (R = .60, P less than .05). Thus, lower initial calcium and calcitonin levels, higher initial levels of 1,25-D, and a greater drug-induced suppression of 1,25-D were associated with an enhanced hypotensive response to verapamil. Verapamil elevated Ca++i0 (2.46 +/- 0.04 to 2.53 +/- 0.04 2.00 mEq/L, P less than .05), and suppressed Mg (2.00 +/- 0.03 to 1.84 +/- 0.03 mEq/L, P less than .01) and 1,25-D levels (66.7 +/- 8.1 to 51.6 +/- 5.7 pg/mL, P less than .05). These results suggest interactive effects of sodium and calcium metabolism in essential hypertension, especially among salt-sensitive individuals. We conclude that alterations of calcium metabolism may underlie the sensitivity to verapamil therapy and may contribute to its hypotensive effects.

Blood Pressure↗
PubMed1989

Hydrochlorothiazide is not additive to verapamil in treating essential hypertension.

Calcium channel blockers, a newer class of antihypertensive medications, have gained considerable acceptance as monotherapeutic agents, particularly in low renin hypertension where diuretics are also most effective. To study whether thiazide diuretics exert an additional antihypertensive effect in the setting of calcium channel blockade, we gave verapamil hydrochloride (360 mg/d) or hydrochlorothiazide (25 mg/d) alone and in combination in an open study to 13 hypertensive patients with mild to moderate essential hypertension. Both verapamil and hydrochlorothiazide lowered blood pressure (170 +/- 17/109 +/- 6 mm Hg pretreatment to 150 +/- 25/95 +/- 8 mm Hg with verapamil; 170 +/- 5/109 +/- 2 mm Hg pretreatment to 164 +/- 25/103 +/- 10 mm Hg with hydrochlorothiazide), but addition of hydrochlorothiazide to verapamil resulted in no added benefit (150 +/- 25/95 +/- 8 mm Hg vs 150 +/- 20/95 +/- 6 mm Hg). Furthermore, while hydrochlorothiazide lowered serum potassium values (4.2 +/- 0.25 mmol/L to 3.7 +/- 0.35 mmol/L) and stimulated plasma renin activity (1.5 +/- 1.3 ng/mL/h) pretreatment to 3.3 +/- 2.7 ng/mL/h with verapamil), verapamil only modestly elevated renin activity (1.5 +/- 1.3 ng/mL/h pretreatment to 2.7 +/- 2.5 ng/mL/h with verapamil) and did not lower potassium values. Altogether, the data suggest that in essential hypertension, at least for verapamil, concurrent diuretic therapy may not be helpful or warranted.

Blood Pressure↗
PubMed1988

The antihypertensive effects of calcium channel blockade: role of sodium and calcium metabolism.

To study the relation of calcium channel blockade to sodium and calcium metabolism, we measured blood pressure (BP), serum ionized calcium (Ca-io), plasma renin activity (PRA), and 1,25-dihydroxy-vitamin D (1,25D), before and after administration of nitrendipine to essential hypertensive (EH) outpatients on both low and high dietary salt intakes, and on fixed (10 mg b.i.d.) and titrated dose (10-30 mg b.i.d.) schedules. Nitrendipine lowered BP (% delta DBP = -14.9 +/- 3 vs. 1 +/- 3.5, p less than 0.001) and raised Ca-io (0.08 +/- 0.04 vs. -0.04 +/- 0.05 mEq/L, p less than 0.05) in salt-sensitive (SS) but not salt-insensitive (SI) subjects. % delta DBP was related to PRA (r = 0.69, p less than 0.001), to the rise in Ca-io (r = -0.63, p less than 0.01), and to the suppression of circulating 1,25D (r = 0.80, p less than 0.001). Similarly, at doses (10-30 mg b.i.d.) titrated to achieve normotension, nitrendipine uniformly elevated PRA (1.4 +/- 0.3 to 3.5 +/- 0.7 ng/ml/h, p less than 0.05) and Ca-io (2.34 +/- 0.02 to 2.44 +/- 0.02 mEq/L, p less than 0.05). We conclude that the antihypertensive efficacy of nitrendipine appears greatest among SS and lower renin patients, and is related to the drug's ability to alter calcium metabolism. The state of calcium metabolism may thus underlie the sensitivity to calcium blockade and may contribute to its effects.

Blood Pressure↗
PubMed1987

Calcium, the renin-aldosterone system, and the hypotensive response to nifedipine.

Ionic, hormonal, and blood pressure responses to a single oral dose of the calcium channel blocker nifedipine were assessed in 25 essential hypertensive subjects. When grouped according to their renin-sodium profile, low renin subjects had a greater hypotensive response to nifedipine (change in diastolic blood pressure -20.0 +/- 1.4 vs -6.4 +/- 1.0%; p less than 0.005) than did high renin hypertensive subjects. The initial level of serum ionized calcium predicted the blood pressure response to nifedipine (r = 0.70, p less than 0.001), as did the initial plasma renin activity (r = 0.65, p less than 0.005). Nifedipine induced a transient rise in serum ionized calcium (from 2.22 +/- 0.02 to 2.28 +/- 0.02 mEq/L; p less than 0.01), while plasma renin activity was consistently elevated compared with initial values at 30 (p less than 0.01), 60 (p less than 0.01), and 120 (p less than 0.05) minutes after drug administration. By comparison, plasma aldosterone levels did not rise and even declined at 30 (p less than 0.01), 60 (p less than 0.05), and 120 (p less than 0.05) minutes after nifedipine. These results suggest that low renin hypertension is more critically dependent on extracellular calcium than are higher renin forms and demonstrate that levels of serum ionized calcium, plasma renin activity, or both may predict the sensitivity of blood pressure to calcium channel blockade. Lastly, calcium may play a pivotal role in vivo in coupling renin stimulation to adrenal aldosterone responses.

Aldosterone↗
PubMed1987

The antihypertensive effect of verapamil at extremes of dietary sodium intake.

Restricting sodium intake is a primary recommendation for patients with hypertension, including those receiving drug treatment. Few studies, however, have examined the impact of different levels of sodium intake on the effectiveness of antihypertensive drugs. We administered two courses of verapamil to 13 patients with essential hypertension during a low-sodium (NaCl, 9 meq/d) and high-sodium (212 meq/d) diet. Overall, verapamil was an effective antihypertensive agent, but expressed its greatest potency in the lower-renin, sodium-sensitive subgroup. Moreover, the antihypertensive efficacy of verapamil was not blunted by the high-sodium intake (change in systolic/diastolic blood pressure, 18.8/17.7 in sodium sensitive patients compared with -11.4/-8.7 in sodium insensitive patients; p less than 0.05). Thus, dietary sodium restriction may not be necessary or appropriate in the treatment of essential hypertension with verapamil; salt-induced cellular calcium uptake may be involved in the phenomenon of sodium sensitivity.

Adult↗
PubMed1986

Calcium metabolism in essential hypertension: relationship to altered renin system activity.

Hypertensive disease is associated with various abnormalities of calcium metabolism although how these abnormalities relate to the elevated pressure remains unclear. Based on the use of renin-sodium profiling, we have defined heterogeneous deviations in circulating levels of ionized calcium and magnesium as well as of the calcium-regulating hormones parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D (1,25D), which parallel similar deviations in plasma renin activity. Essential hypertensive subjects with a profile of low renin, lower ionized calcium, and elevated 1,25D respond best to the calcium channel blocker nifedipine, demonstrate an enhanced sensitivity to the blood pressure effects of dietary salt loading, and have significantly lower blood pressures in response to oral calcium supplementation. Hypertensive subjects with the opposite metabolic profile--higher renin activity, higher serum ionized calcium, and lower 1,25D levels--are relatively insensitive to the blood pressure effects of either dietary salt loading or nifedipine, and show no significant hypotensive response to calcium supplements. Altogether, these alterations of calcium ionic and hormonal metabolism suggest that the hormonal control of calcium metabolism is linked to renin system activity as well as to the pathophysiology of the hypertensive process.

Calcitonin↗
PubMed1985

Relationship of blood pressure response and the renin-angiotensin system to first-dose prazosin.

It has been reported that the first-dose response to prazosin is more common in patients who are salt-depleted or already receiving beta blockers. The relationship between the first-dose blood pressure and plasma renin responses to oral administration of 1 mg prazosin in 13 (seven male, six female) patients with essential hypertension (average blood pressure = 150/100 +/- 5/2 mm Hg) was studied. Eight of 13 patients experienced marked orthostatic decreases in blood pressure associated with nausea and dizziness. The degree of the orthostatic depressor response was inversely correlated with the baseline plasma renin activity (p less than 0.005). This unique sensitivity of low-renin essential hypertension to prazosin may reflect an underlying increased alpha tone and/or an attendant blunted renin reactivity in this form of human essential hypertension.

Blood Pressure↗
PubMed1985

Calcium metabolism and the renin-aldosterone system in essential hypertension.

Despite recent appreciation of a role for calcium in clinical hypertension, evidence at present is conflicting. Thus, certain studies suggest increased calcium availability may be associated with increased levels of blood pressure, while others suggest that a calcium deficiency may contribute to the pathogenesis of hypertensive disease. Our own group has thus far demonstrated deviations of circulating levels of ionized calcium and of magnesium in essential hypertension, linked with concurrent deviations in the activity of the renal pressor hormone, renin. Furthermore, calcium metabolic indices may predict and even determine dietary sodium sensitivity in hypertension, as well as the blood pressure responsiveness to antihypertensive drug therapy. Moreover, oral calcium supplementation may itself possess antihypertensive actions in specifically targeted renin subgroups of essential hypertensive subjects. Altogether, these results link calcium metabolism, renin system activity, and the pathogenesis of hypertensive disease. It may ultimately be calcium-regulating hormones, which determine cellular disposition of calcium, rather than circulating levels of calcium itself, that mediate the blood pressure and possibly even the renin deviations observed among differing hypertensive individuals.

Aldosterone↗