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Electrocardiography and Carbohydrate Metabolism: II. P Wave Height Lead in Presumably Healthy Young Men
Published in Angiology, Vol. 21, No. 1, January 1970.
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There is increasing awareness of relationships between cardiovascular disease and carbohydrate metabolism.1-10 Within this area, there are several reports which note interesting correlations between electrocardiography and carbohydrate metabolism.11-15 An earlier report in this series analyzed the duration of the P-wave in lead I with regard to postprandial blood glucose.16 This paper, the second in the series, correlates another electrocardiographic parameter in presumably healthy young men with postprandial blood glucose. Specifically, an attempt will be made to answer the following three questions. (1) How reproducible is the measurement of P-wave height in lead I? (2) How constant is P-wave height (lead I) recorded 4 days apart in a group of presumably healthy young men consuming a regular diet? (3) Is there any relationship between the P-wave height (lead I) and blood glucose in healthy young men subsisting on a regular dietary regime for 4 days?
Method of Investigation
Thirty-eight presumably healthy junior dental students participated in this study. On a Monday, routine electrocardiography (leads I to III) was performed at about 10:00 a.m. In addition, a 3-hr. postprandial blood glucose (Somogyi-Nelson method)17, 18 was determined. On Friday of the same week at 10:00 a.m., electrocardiograms were again recorded and blood glucose assays were repeated.
The electrocardiographic patterns were read under a dissecting microscope with a magnification of 60x.19 Each measurement was repeated (to ensure accuracy) by the same examiner, with no knowledge of the student’s name, electrocardiographic lead or visit number.
Results
Question 1. An attempt was first made to establish the constancy of the measuring technique. Table 1 lists the first and second P-wave height readings at the initial and final visits. Of the 76 duplicate measurements, 43 were different (table 2). Of these 43, 37 varied by 0.1 mm and 6 by 0.2 mm. The significant (p < 0.01) coefficient of correlation (r = +0.927) attests to the reproducibility of the measuring technique. Hence, a high degree of accuracy was achieved in measuring the P-wave height in lead I.
Question 2. How constant is the P-wave height (lead I) during a 4-day interval in healthy young men subsisting on a regular diet? Table 3 lists the mean initial and final P-wave heights. The coefficient of correlation proved to be -0.051, and its lack of significance is underscored by p > 0.05. Apparently, healthy young men subsisting on a regular diet did not show a constant electrocardiogram as expressed in P1-wave height.
Question 3. It is abundantly clear that the P-wave height in lead I fluctuated from day to day. Although some of the changes may have been due to the method of measurement, undoubtedly other factors were also operative. The question now to be answered is whether there is any relationship between the P-wave height in lead I and carbohydrate metabolism. To answer this question, one must first examine the blood glucose levels recorded on Monday and Friday in these students.
Table 3 summarizes the nonfasting blood glucose determinations at these two visits. The initial and final values are 80.4 ± 9.3 and 81.9 ± 10.9 mg/100 ml, respectively. The lack of statistical significance is underscored by a coefficient of correlation of +0.253 and p > 0.05. Hence, it is obvious that blood glucose varied during the experimental period.
Figure 1 describes the differences in the initial and final values in P-wave height on the abscissa and those for blood glucose on the ordinate. The correlation coefficient of -0.385, p < 0.05, suggests that fluctuations in the electrocardiographic pattern paralleled changes in P1-wave height. In other words, when blood glucose rose, P1-wave height decreased. Conversely, when blood glucose declined, P1-wave height rose. Thus, healthy young men subsisting on a regular diet demonstrated a significant negative relationship between P1-wave height and blood glucose.
Fig 1. The relationship of change in blood glucose and P1-wave height during 3 days. The evidence suggests that, as blood glucose rises, P-wave height diminishes.
Discussion
In an earlier report,16 it was shown that there was a significant reproducibility of P1-wave length as shown by a correlation coefficient of +0.961, significant at the 1 per cent confidence level. There is also a statistically significant reproducibility in measuring P1-wave height as shown in this report by an r = ± 0.927 and a p < 0.01. However, with regard to P1-wave length, 86.8 per cent of the duplicate measurements were identical, whereas here in connection with P1-wave height, the frequency of identical readings was only 43.4 per cent. Hence, the conclusion may be drawn that P-wave height is not as reproducible as P-wave length.
It was shown earlier16 that P1-wave length varied considerably from day to day, as shown by a statistically insignificant (p > 0.05) correlation coefficient of +0.260. It has been reported in this study that there is also great fluctuation in the electrocardiographic P1-wave height from day to day as demonstrated by an r = -0.051 and p > 0.05. Hence, the fluctuations in P-wave height seem to be greater than those in P-wave length. Part of the explanation may be the greater difficulty in measurement of height versus length.
Finally, evidence has been offered16 that the variation of P1 length parallels the change in blood glucose only when the sign is disregarded. In contrast, the data with P1-wave height suggest more orderly electrocardiographic and biochemical parallelisms. Thus, when P-wave height decreased, blood glucose rose. Conversely, when P-wave height increased, blood glucose increased.
Dubos,20 in his writings about Claude Bernard and homeostasis, made the following relevant statement.
“He (Claude Bernard) emphasized that at all levels of biological organization, in plants as well as in animals, survival and fitness are conditioned by the ability of the organism to resist the impact of the outside world and maintain constant within narrow limits (italics added) the physicochemical characteristics of its internal environment.”
On the assumption that the steady state is indeed steady, the evidence here suggests that the inconstancy of the P1-wave height and blood glucose significantly correlate.
Summary
- Thirty-eight presumably healthy junior dental students participated in this experiment, in which the height of the P-wave in lead I and blood glucose by the Somogyi-Nelson method were determined at 10:00 a.m. on Monday and Friday of the same week.
- The evidence suggests that the measurement of P1-wave height is highly reproducible. Also, the data suggest that, for the group, P-wave height and blood glucose are quite inconstant from Monday to Friday.
- It is fair to assume from the information available in this report that a significant negative relationship exists between P-wave height in lead I and blood glucose.
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