There are several major reasons why blood pressure should be measured at the workplace:
1) Public Health - Surveillance of the workplace to determine the prevalence of hypertension or elevated blood pressure is important from a public health perspective, especially in light of the evidence that workplace factors play a significant role in the etiology of essential hypertension. Worksite screenings are the only way to identify those groups of individuals with normal clinic BP and elevated worktime BP, the "false negatives" - who are at a high risk for a hypertension related morbid event.
2) Improved Clinical Diagnosis - Collecting worksite estimates of BP should result in improved diagnosis and treatment of patients. The level of an individual's worktime BP is important for diagnosis, as a predictor of subsequent illness and for evaluation of clinical treatment.
3) Studies of etiology - To the extent that psychosocial workforce factors play an important etiologic role in the genesis of hypertension, where one measures BP matters, because these factors are not static and may or may not be present at any moment. All BP measures are influenced by some set of psychosocial factors. For example, BP in the clinic is subject to the "white coat" effect. BP at home can be affected by home stressors and likely carry-over from work. Sleep BP may be influenced by dreaming (REM sleep), which is associated with elevation of BP and disinhibition of CV control mechanisms (Bond et al., 1973). Factors such as work-related stressors, physical activity, and posture are important in workplace BP assessment.
A significant association has also been found between left ventricular mass index and exposure to job strain (Schnall et al., 1990). Left ventricular enlargement is correlated more highly with average BP at A significant association has also been found between left ventricular work than at other locations (Devereux et al., 1983; Baba et al., 1988; Devereux and Roman, 1995). These authors propose that the observed associations between job strain, left ventricular hypertrophy, and hypertension suggest a pathophysiologic process that may explain the reported association between job strain and CHD mortality. Measurement of BP at the workplace represents the critical node for further elucidating these inter-relations.
4) Reliability and validity of workplace AmBP's are more reliable and have greater validity than casual clinic BPs, and this may also be true for point estimates of worktime BP.
5) Reduced cost - It is usually less expensive to collect BP at the workplace than to send individuals to a medical center.
Basal Blood Pressures
The concept of casual BP is derived from the work of Smirk (Smirk, 1944) in the 1940's. His idea was that the clinic BP had two independent components - the basal and the supplemental. Basal BP's were those obtained in a seated subject in a comfortable environment after a 30' wait by a single observer. The difference between this BP and the initial BP (the casual BP) was supplemental BP. Smirk found that Basal BP's and supplemental readings did not correlate. It was proposed that the basal BP represented the structural or fixed elements of an individual's hypertension, while the supplemental pressure was the elevation attributable to the effects of physical and mental activity.
The fact that casual BP was uncorrelated with basal BP in Smirk's research requires explication. It is plausible that the psychosocial, mental and physical factors associated with a visit to the doctor's office reflect a small percentage of actual exposures impacting on an individual's basal tonic BP. In contrast, picture a universe of exposures that influence one's BP (the frequency and intensity of these exposures will determine the ultimate impact on one's BP). Work stressors, since they occur more frequently (longer hours of the days, more days of the year, more years of a life) and with greater intensity than does the stress of a doctors' office visit, will play a major role in elevating an individual's BP (Schnall, et al., 1998).
The possibility of obtaining a basal BP uninfluenced by psychosocial factors seems unlikely. There is a real question whether 30 minutes or more (rarely achieved in practice) of rest in a comfortable environment is a true reflection of basal BP. Even under such conditions humans are not free of psychosocial influences. In fact, we have often observed increases in BP in patients at rest (anxious subjects may worry increasingly as they "rest"). Even among those persons who manage to fully relax and shut out nearly all psychosocial stimuli, this approximation of basal BP may not necessarily be reflective of clinically relevant BP status.
The very concept of basal BP - a BP free of all psychosocial and other stimuli providing a best estimate of tonic true BP - is not compatible with our current notions of the etiology of essential hypertension of neurogenic origin. We now believe that in most cases of essential hypertension, psychosocial factors, especially at work, will play an important role in elevation of BP. Basal BP eventually reflects these influences. This process leads to three identifiable stages: 1) When individuals first are exposed to putative causes such as workplace stressors, BP's are elevated at work while basal BP are normal. 2) Chronic exposure to these stressors lead to elevated workplace BP's as well as basal BP's (Folkow, 1987, Folkow, 1994). At this stage the psychosocial factors likely are correlated with both measures of BP (structural changes in the cardiovascular system are occurring). 3) In end-stage hypertension, self-sustaining structural processes in the vascular system may lead to disjuncture between reported psychosocial factors and BP (both workplace and basal) since the individual may no longer be exposed to the psychosocial factors (e.g., promotion, retirement) and the BP process is now autonomous.
These stages are consistent with the presumed mechanisms of neurogenic hypertension - an initial reversible stage with predominant elevation of systolic BP as the defense response is elicited. With repeated exposure, structural changes occur in the heart and vasculature (ibid).
Problems with Clinic Measures
In the clinic setting there are a number of new psychosocial stimuli present that can affect BP. For some individuals the presumably unpleasant experience of the clinic setting can produce an elevation. This may be a unique response (i.e., totally unrelated to one's usual universe of BP's during daily life). It has been called the "white coat" phenomenon and is characterized by normal ambulatory BP and high clinic casual BP. Most studies of individuals who display this unique response appear to show they are at relatively low risk for morbid events compared to those with sustained hypertension (Pickering 1995). However, Julius et al (1990) argue to the contrary, on the basis of point measurements at home vs. clinic. They found an increased prevalence of cardiovascular metabolic syndrome (SPNS driven) among the young adults with white coat hypertension, and postulate that white coat hypertension is mediated by over-activity of the SNS.
According to Pickering "true blood pressure may be regarded as the average level over a prolonged period of time, which is generally thought to be the most important determinant of target organ damage" (Pickering, 1991). The interest in and subsequent research with AmBP monitoring arose out of the observation that the typical casual clinic BP is highly variable and does not reliably reflect BP during daily life. A body of evidence that ambulatory workplace BP (AmBP) is a better predictor of morbidity and mortality has emerged. BP's obtained with an AmBP monitor are more reliable and valid than other assessments of BP.
Combining information from both casual clinic BP's and AmBPs allows identification of four groups - two in which the clinic BP and AmBP agree and two crossover groups:
Individuals with normal clinic BP but elevated AmBP are the false positives (i.e. those with white coat hypertension) if one accepts AmBP as the definitive measure of BP.
Individuals with normal clinic Bp but elevated AmBP are the false negatives. This group is potentially at risk of an untoward event since AmBP's are increased and yet these individuals remain undiagnosed. It has been found, for example, that among individuals in stressful professions (e.g., journalists and professional drivers) selected to have normal clinic BP, worktime DBP averaged to be nearly 90 mmHg and some individuals had sustained increases in work BP that failed to decrease below 150/100 during the entire recording period (Ugljesic, et al., 1992). Obtaining estimates of BP at the workplace in such individuals would be extremely important from a clinical perspective and alone is justification for worksite BP screenings.
Problems with Ambulatory Measures
First, logistics at the workplace frequently are complicated. Participants wearing a monitor require time to don the equipment, will experience frequent interruptions of work - albeit of short duration - when BP is measured and a diary filled out, and need time to remove the monitor at the end of the work period. For some work activities these interruptions may have serious consequences for job performance and productivity especially when large numbers of participants are involved.
Second, costs are high for several reasons. Equipment, including the monitors themselves and the necessary computers, are expensive. Moreover, AmBP measurement is a technologically sophisticated and labor-intensive process requiring highly trained personnel to collect and process data. Trained technicians hook the subject up to the equipment; insure its proper working; explain its use to the wearer, including the completion of an accompanying diary (for location and activity codes); and enter and code the obtained data into a computer.
Point Estimates as an Alternative to AmBP monitoring
What is needed is a point estimate of BP that approximates a typical AmBP reading in the same subject. We can imagine a subject wearing an AmBP monitor at work and wanting to obtain several readings during the same period, which approximate those that the machine is obtaining when it records BP every 15 minutes or so during the working day.
Advantages
Disadvantages
Protocol for obtaining a "point estimate" of Worktime BP
Part 1: Checklist. Use prior to obtaining point measurements
at the workplace - before the workday on which BP is to be measured:
1. Obtain informed consent
2. Obtain arm circumference
3. Provide instructions regarding clothing (e.g. loose shirts,
accessible arms, etc.)
4. Collect medication and medical history (and other relevant
data)
5. Use simplest accurate equipment - a carefully calibrated Anaeroid
device (not a mercury column)
Part 2: BP Protocol for obtaining two sets of point estimates. Conducted while individuals are working.
1. Trained observer can measure (not necessarily health professional)
2. Avoid "clinic atmosphere" - no white coats; don't
act like a clinician
3. Aim for informal interactions and neutral conversations - avoid
conversations that are of personal relevance to the participant;
do not discuss controversial issues until after BP collection.
4. Obtain two sets of point estimates in one workday while subject
is at usual work activity.
5. Equipment: calibrated aneroid sphygmomanometer (determine
proper cuff size)
6. Conducting actual point estimate measurements
7. Average first and second readings for best estimate; discard
third.
8. Subject feedback
Part 3. Protocol for obtaining related data. Needed to complement point estimate of BP at the workplace.
1. Diary
2. Medical history, demographics, and other potential confounders
3. Data analysis (depends on purpose of measurement)
4. Some unresolved questions
References
American Heart Association: Blood pressure testing and measurement (http://www.americanheart.org/Heart_and_Stroke_A_Z_Guide/), American Heart Association, 1998
Baba S, Nakamoto Y, Ueshima H, Ozawa H, Omae T: Variations of blood pressures under regularly recurring stress in daily life and its relation to left ventricular hypertrophy in urban hypertensive men. Journal of Hypertension 6:S695-S696, 1988
Bond WC, Bohs C, Ebey Jr J, Wolf S: Rhythmic heart rate variability (sinus arrhythmia) related to stages of sleep. Conditional Reflex 8:98-107, 1973
Devereux RB, Pickering TG, Harshfield GA, Kleinert HD, Denby L, Clark L, Pregibon D, Jason MN, Kleiner B, Borer JS, Laragh JH: Left ventricular hypertrophy in patients with hypertension: importance of blood pressure response to regularly recurring stress. Circulation 68:476-479, 1983
Devereux RB, Roman MJ: Hypertensive cardiac hypertrophy: pathophysiologic and clinical charactersitics. In Laragh JH, Brenner BM (eds), Hypertension: Pathophysiology, Diagnosis, and Management. New York, Raven Press, Ltd., 1995, 409-432
Folkow B: Psychosocial and central nervous influence in primary hypertension. Circulation 76:10-9, 1987
Folkow B: Autonomic Nervous System in Hypertension. In Swales JD (ed), Textbook of Hypertension. London, Blackwell Scientific Publications, 1994, 427-438
Julius S, Mejia A, Jones K, Krause L, Schork N, van de Ven C, Johnson E, Petrin J, Sekkarie MA, Kjeldsen SE, Schmouder R, Gupta R, Ferraro J, Nazzaro P, Weisfeld J: "White coat" versus "sustained" borderline hypertension in Tecumseh, Michigan. Hypertension 16:617-623, 1990
Pickering TG: Ambulatory monitoring and blood pressure variability. London, Science Press, 1991
Schnall PL, Landsbergis PA, Schwartz J, Warren K, Pickering TG: A longitudinal study of job strain and ambulatory blood pressure: Results from a three-year follow-up. Psychosom Med 60:697-706, 1998a
Schnall PL, Pieper C, Schwartz JE, Karasek RA, Schlussel Y, Devereux RB, Ganau A, Alderman M, Warren K, Pickering TG: The relationship between 'job strain,' workplace diastolic blood pressure, and left ventricular mass index. Results of a case-control study [published erratum appears in JAMA 1992 Mar 4;267(9):1209]. JAMA 263:1929-35, 1990
Smirk FH: Casual and Basal Blood Pressures IV. Their relationship to the supplemental pressure with a note on statistical implications. British Heart Journal 6:174-182, 1944
Ugljesic M, Belkic K, Boskovic S, Avramovic D, Mickovic L: Porast arterijskog krvnog pritiska tokom rada i profil rizika kod stresogenih profesija: novinari i vozaci gradskog saobracja (Increased arterial blood pressure during work and risk profile among high-stress occupations: journalists and city mass transit drivers). Kardiologija 13:150-154, 1992