Regional coronary hemodynamic responses during the cold pressor test: lack of effect of nitroglycerin

Coronary blood flow after cold exposure and the effect of warm-up exercise

BACKGROUND

Cold pressor test (CPT) results indicate that coronary blood flow (CBF) increases after sudden cold exposure. Traditionally, warm-up exercise (WEx) has been recommended before cold exposure; however, the physiologic effects of WEx on CBF have not been elucidated. Therefore, this study was undertaken to evaluate the effect of WEx on CBF after cold exposure.

METHODS

Fifteen healthy young men were enrolled in this study. CBF at the distal left anterior descending coronary artery was assessed by transthoracic Doppler echocardiography at baseline and after CPT. The same measurements were made with WEx and weight-bearing exercise before CPT after a 20-minute recovery period between each measurement. In the CBF velocities, the time-velocity integral of diastolic flow (Dtvi) was measured in addition to blood pressure and heart rate (HR).

RESULTS

The product of Dtvi x HR increased significantly after CPT. Increments in Dtvi x HR after CPT with WEx before CPT were significantly higher than CPT alone (130 +/- 82% vs 68 +/- 37%, P < .05). However, increments in Dtvi x HR after CPT with weight-bearing exercise before CPT were not significantly different from those observed for CPT alone (74 +/- 50% vs 68 +/- 37%, P = not significant).

CONCLUSION

Our study suggests that WEx can augment an increased CBF after cold exposure. This augmentation of CBF increase after cold exposure may help the body meet increased physiologic demands imposed on it by cold exposure. However, this phenomenon was not observed for anaerobic weight-bearing exercise.

A new noninvasive method of diagnosing vasospastic angina based on dilation response of the left main coronary artery to nitroglycerin as measured by echocardiography

OBJECTIVES

The purpose of the present study was to evaluate the feasibility of diagnosing vasospastic angina based on coronary artery tone as assessed by M-mode echocardiographic measurement of the dilation response of the left main coronary artery to nitroglycerin.

BACKGROUND

The definite diagnosis of vasospastic angina is done by a coronary spasm provocative test using ergonovine maleate or acetylcholine during cardiac catheterization. Current noninvasive, nonpharmacologic diagnostic methods are not sensitive enough for the diagnosis of vasospastic angina.

METHODS

Thirty-eight patients who had an angiographically normal left main trunk were studied. These patients were classified into four groups based on the presence or absence of more than 50% stenosis in the coronary arteries except for the left main trunk and the results of the acetylcholine or ergonovine provocative test. At 7 a.m. and at noon on the same day, the left main trunk diameter was measured by M-mode echocardiography before and after sublingual administration of nitroglycerin (0.3 mg), and its present dilation was calculated to assess coronary artery tone.

RESULTS

The percent dilation of the left main trunk diameter induced by sublingual nitroglycerin at 7 a.m. and at noon was 22.4 +/- 4.7% (mean +/- SD) and 18.1 +/- 4.0% in 11 patients with vasospastic angina and without coronary stenosis, 14.9 +/- 7.1% and 11.2 +/- 6.9% in 9 patients with vasospastic angina and coronary stenosis, 6.1 +/- 3.5% and 7.0 +/- 5.1% in 8 patients without vasospastic angina but with coronary stenosis and 8.1 +/- 5.6% and 7.8 +/- 5.7% in 10 control subjects. The percent dilation at 7 a.m. was significantly greater in the vasospastic angina without coronary stenosis group than in the remaining three groups, and in the vasospastic angina groups, the percent dilation at 7 a.m. was significantly greater than that at noon. When percent dilation at 7 a.m. exceeding 15% was defined as positive for the diagnosis of vasospastic angina, the sensitivity was 80% and the specificity 94%.

CONCLUSIONS

Basal tone of the left main trunk is elevated in the early morning in vasospastic angina. Dilation of the left main trunk diameter exceeding 15% induced by sublingual nitroglycerin in the early morning as measured by M-mode echocardiography is a highly sensitive and specific criterion for the diagnosis of vasospastic angina.

Daily life ischemia and nitrate therapy

Daily life ischemia has generated considerable interest because most of it is silent and associated with increased risk of adverse outcome. Coronary vasomotion, as well as increases in myocardial oxygen demand, seem important in the pathogenesis of this form of ischemia, so treatment with nitrates seems rational. Administration of sublingual nitroglycerin hourly, over 12 hours, was shown to decrease both silent and painful ischemic episodes in patients with effort angina. Subsequently, isosorbide dinitrate or mononitrate, given either as an intravenous infusion or orally, was shown to decrease both silent and painful ischemic episodes in patients with unstable rest angina and in those with severe angina. More recently, 6 studies have reported using transdermal nitroglycerin for daily life ischemia. Three of these reported open-label uncontrolled observations and suggested that ischemia frequency may be reduced approximately 60-80% during treatment with doses of 10-30 mg/day, with a duration of treatment ranging from 1 hour to 14 days. In 2 of these reports the duration of ischemia also decreased. The other 3 studies were randomized, double-blind, placebo-controlled studies with a total enrollment of 86 patients. These studies provided mixed results. One suggested that evidence for partial tolerance develops within 1 day of treatment, using large continuous or intermittent doses (mean, 52 mg/day). Another suggested that no tolerance develops to intermittent dosing (18 mg/16 hr out of 24 hr) during exercise testing but no effect is seen on daily life ischemia. The remaining study suggested that tolerance does not develop using small doses (15 mg/day) continuously over 14 days for ischemia during daily life, and that this response is different from that observed using the calcium antagonist nifedipine. These limited observations and conflicting results underscore a need for additional larger controlled trials, employing topical nitrate therapy in low intermittent doses for daily life ischemia.