Cardiovascular Risk Factors

Blood Pressure

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Description
Blood pressure is an index of cardiovascular activity. There are two indicators of blood pressure. The systolic pressure is the maximum pressure in an artery at the moment when the heart is beating and pumping blood through the body. The diastolic pressure is the lowest pressure in an artery in the moments between beats when the heart is resting.

Both the systolic and diastolic pressure measurements are important - if either one is raised, it indicates high blood pressure (hypertension). Systolic blood pressure is generally more related to aging outcomes. Generally risk levels are indicated by a systolic blood pressure >140 or a diastolic blood pressure >90 (http://alzheimers.about.com/od/treatmentoptions/a/blood_pressure.htm?terms=blood+pressure).

Over a ten-year period, a 10 mm Hg increase in diastolic pressure is associated with a 31% increase in risk of cardiovascular death associated (Glynn et al., 1995), a 127% increased risk for incident stroke (MacNahon et al., 1990) and 59% for incident coronary heart disease (MacNahon et al., 1990).

Significance of Measurement
Elevated systolic pressure and elevated diastolic pressure predict increased risks of cardiovascular death. Systolic pressure is also significantly associated with risk of total mortality in the elderly (Glynn et al., 1995).

Method of Measurement
To take a blood pressure reading, a cuff that inflates is wrapped around the upper arm. The pressure in the cuff is shown on the mercury column. Air is blown into the cuff to increase pressure and a stethoscope is placed on the arm. Systolic pressure is measured when sound is heard. The diastolic pressure is measured at the moment the sound is no longer heard. Blood pressure is measured in terms of millimeters of mercury (mmHg). Blood pressure can also be measured using an automatic blood pressure gauge.

In research settings, these measures are usually taken 3 or 4 times. The first measurement is often eliminated and blood pressure is recorded as the average of the last 3 readings.

References
· Kennard, C. (n.d.). Blood pressure explained. Retrieved March 28, 2005, from http://alzheimers.about.com/od/treatmentoptions/a/blood_pressure.htm?terms=blood+pressure
· MacNahon, S., Peto, R., Cutler, J., Collins, R., Sorlie, P., Neaton, J., et al. (1990). Blood pressure, stroke, and coronary heart disease. Part I, Prolonged differences in blood pressure: Prospective observational studies corrected for the regression dilution bias. Lancet, 335, 765-774
· Glynn, R.J., Field, T.S., Rosner, B., Hebert, P.R., Taylor, J.O., & Hennekens, C.H. (1995). Evidence for a positive linear relation between blood pressure and mortality in elderly people. Lancet, 345(8953), 825-829.

Heart Rate Variability

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The following information has been gathered from the MacArthur Research Network on Socioeconomic Status and Health (http://www.macses.ucsf.edu/Research/Allostatic/notebook/heart.rate.html).
Please refer to this website for more details.

Description
Heart rate variability (HRV) refers to the beat-to-beat alterations in heart rate. Under resting conditions, the Electro Cardiogram (ECG) of healthy individuals exhibits periodic variation in R-R intervals. This rhythmic phenomenon, known as respiratory sinus arrhythmia (RSA), fluctuates with the phase of respiration -- cardio-acceleration during inspiration, and cardio-deceleration during expiration. RSA is predominantly mediated by respiratory gating of parasymphathetic efferent activity to the heart: vagal efferent traffic to the sinus node occurs primarily in phase with expiration and is absent or attenuated during inspiration and is absent or attenuated during inspiration

Significance of Measurement
The major reason for the interest in measuring HRV stems from its ability to predict survival after heart attack. Over half a dozen prospective studies have shown that reduced HRV predicts sudden death in patients with MI, independent of other prognostic indicators such as ejection fraction.

Method of Measurement
Originally, HRV was assessed manually from calculation of the mean R-R interval and its standard deviation measured on short-term (e.g., 5 minute) electrocardiograms. The smaller the standard deviation in R-R intervals, the lower is the HRV. To date, over 26 different types of arithmetic manipulations of R-R intervals have been used in the literature to represent HRV. The measurement of HRV is becoming increasingly standardized.

References
· John, D., & Catherine, T. MacArthur Research Network on Socioeconomic Status and Health. (2000). heart rate variability. Retrieved March 25, 2005, from http://www.macses.ucsf.edu/Research/Allostatic/notebook/heart.rate.html