Study of 120 healthy subjects without cardiovascular disease, 40 smokers of conventional cigarettes, 40 exclusive users of Heat-non-Burn Cigarettes and 40 nonsmokers.~All subjects are civil medical personnel working for the National Health System, in a Tertiary University Hospital in Athens. Also, working in a hospital environment will ensure the use of a mask during the shift.~Baseline measurements of CO will be performed in the morning after awakening without the use of any mask when they arrived at hospital. This time point is selected to detect the lowest exhaled CO levels after the abstinence of smoking during the sleep. CO has a half-life of 5-6 hours and consequently CO levels after the period of sleep (almost 8 hours) verge to decline or to normalize.~After baseline CO measurement, subjects will be randomly assigned to assess exhaled CO concentration at the end of an 8h morning shift wearing a mask at hospital, or to CO assessment at the end of an 8h morning period without mask out of the hospital (usually home stay). Then the subjects will be crossed over to CO assessment at end of an 8h period without mask out of the hospital after their shift or to an 8h afternoon period wearing a mask during an afternoon hospital shift respectively.~Measurements with and without mask will be done one hour after smoking the last cigarette. Subjects are inducted to smoke the same number of cigarettes or heets during their shift while wearing the mask as well as during the out-hospital period when not using a mask. During their shift they are instructed to wear the surgical mask constantly.
Study of 120 healthy subjects without cardiovascular disease, 40 smokers of conventional cigarettes, 40 exclusive users of Heat-non-Burn Cigarettes and 40 nonsmokers.~Baseline measurements of CO will be performed in the morning after awakening without the use of any mask when they arrive at hospital. This time point is selected to detect the lowest exhaled CO levels after the abstinence of smoking during the sleep.~After baseline CO measurement, subjects will be randomly assigned to assess exhaled CO concentration at the end of an 8h morning shift wearing a mask at hospital, or to CO assessment at the end of an 8h morning period without mask out of the hospital (usually home stay). Then the subjects will be crossed over to CO assessment at end of an 8h period without mask out of the hospital after their shift or to an 8h afternoon period wearing a mask during an afternoon hospital shift respectively.