9-2 Secondhand tobacco smoke increases the risk of a heart attack. In order to investigate the mechanisms for this effect, C. Arden Pope III and his colleagues†

studied whether breathing secondhand smoke affected autonomic (reflex) nervous system control of the heart. At rest the heart beats regularly, about once a second, but there are small beat-to-beat random fluctuations of the order of 100 milliseconds (.1 second) superimposed on the regular interval between heartbeats. This random fluctuation in the length of time between heartbeats is known as heart rate variability and quantified as the standard deviation of interbeat intervals over many beats. For reasons that are not fully understood, reductions in this heart rate variability are associated with increased risk of an acute heart attack. Pope and his colleagues measured heart rate variability in eight healthy young adults before and after they spent 2 hours sitting in the smoking lounge at the Salt Lake City Airport. Table 9-9 shows the observations on the standard deviation of the length of time between beats (in millisecond) measured over the 2 hours before and immediately after sitting in the smoking lounge. Did sitting in the smoking lounge reduce heart rate variability?