Physiology of Angina and Its Alleviation With Nitroglycerin

Figure 1.. Aortic and coronary signals. A, Pressure waveform recorded from the ascending aorta from a study patient. Two systolic peaks are labeled P1 and P2. Augmentation index is calculated as augmented pressure (P2−P1) as a percentage of total pulse pressure, P1. The time to the reflected wave from the foot of the pressure tracing to the inflection point is shown as TR. The area under the curve during systole is the tension-time index (TTI), and the area under diastole is the diastolic time index (DTI). Buckberg index is calculated as BI=DTI/TTI. B, Typical coronary pressure and flow velocity recordings. C, Ensemble-averaged pressure and flow velocity signals (blue lines indicate pressure; red line indicates flow velocity). D, The diastolic velocity–pressure gradient relationship, expressed as raw signals, is shown (bottom left), with the data fitted with a quadratic equation ΔP=0+kv+Sv2, where ΔP is the instantaneous pressure gradient (mm Hg), v is the coronary flow velocity (cm/s), k is the coefficient of pressure loss resulting from viscous friction, and S is the coefficient of pressure loss caused by flow separation or localized turbulence.

Figure 2.. Supine exercise resistance protocol and ST-segment change. Top, Exercise performance summarized cycling resistance in Watts with patients cycling at 60 rpm, at baseline (Base), 50% of the time (t50) to peak exercise (peak) when patients experienced significant limiting symptoms, and continued exercise 1 and 2 minutes after peak. At time peak, half the patients had sublingual nitroglycerin (GTN) administered, and all patients continued to exercise for an extra 2 minutes at the same workload. Bottom, The mean surface ECG ST-segment deviation in millivolts. *Statistical significance, baseline vs peak exercise, P<0.05. ‡Significant difference, peak after nitroglycerin (GTN) vs control.

Figure 3.. Hemodynamics on exercise. Systemic hemodynamic parameters of heart rate, mean aortic pressure, and rate-pressure product (RPP) during study protocol. BP indicates blood pressure; and GTN, nitroglycerin. *Statistical significance, baseline vs peak exercise, P<0.05. †Statistically significant difference between peak and 2 minutes after peak.

Figure 4.. Indexes of wave reflection and beat cycle physiology. Systemic hemodynamic augmentation index, time to the reflected wave, tension-time index, diastolic time fraction, left ventricular (LV) ejection time, and Buckberg index. GTN indicates nitroglycerin. *Statistical significance, baseline vs peak exercise, P<0.05. †Statistical significance, peak exercise vs 2 minutes after nitroglycerin administration, P<0.05. ‡Significant difference, peak exercise after nitroglycerin administration vs control.

Figure 5.. Coronary hemodynamics. Mean distal pressure (Pd) to aortic pressure (Pa) ratio and relative change in coronary flow velocity as a ratio of average peak velocity at individual time points vs baseline. GTN indicates nitroglycerin; and t50, 50% of peak exercise.

Figure 6.. Diastolic coronary velocity–pressure gradient relation. Top, Two time points: 50% of peak exercise (t50) and peak exercise recordings in 1 individual. Bottom, Regression lines that arise from aggregating the k and S coefficients from recordings in all patients. Solid lines represent the control group; dashed lines, those who received nitroglycerin (GTN). Black line indicates baseline; blue, t50; red, peak; purple, 1 minute after peak; and green, 2 minutes after peak. *Statistically significant difference vs baseline of the k coefficient (Table 4 lists all the coefficients).