Circadian (24 hour) biorhythms:
- Blood pressure can rise and fall 20% in 24 hours; lowest first thing in the morning and rises during the day.
- White cell count may rise and fall 50% in 24 hours.
- Pulse rate speeds up in the day and slows at night, by around 10 beats per minute. (The normal resting adult heart beat rate ranges from 60–100 bpm; during sleep a rate of 40-50 bpm is common.)
- Fluctuations in some body chemicals, blood pressure and heartbeat, acid content of blood, oral temperature, calcium in urine, number of red blood cells, levels of hormone cortisol.
- With kidney transplants, the peaks of rejection are: major peak 7 days after operation; when serum is given to suppress rejection, the peaks are at 7, 14 21 and 28 days, with 28 days the highest risk.
- Response to malaria infection and certain bacteria have 7 day rhythms.
- Pneumonia crisis (before penicillin was available) was usually on the 7th or 9th day.
- Cancer cells have lost their biological clock, so can be hit at any time.
- Cancer drugs have to minimise harming normal cells, so killing tumour cells should coincide with low point of healthy cell synthesis cycle.
- Anti-cancer drug adriamycin gives fewer side effects when given at 6am as it does in the evening.
- Anti-cancer drug cisplatin should be given late afternoon when potassium secretion is at its highest to avoid toxic effects on the kidneys.
- When sick cells do have rhythms, they are often desynchronised from healthy cells.
- Asthma attacks: the most sensitive time is when lung tubes are at their narrowest in natural rhythms (i.e. just before waking up). Tubes are at their widest at 4pm to 6pm.
- At present medication timing is usually by hospital clock and averages; perhaps in future this may be tailored to the individual's body clock, with the marker rhythm varying with the disease.
- Studies show breast cancer operations give signficantly better results if carried out in the 13 to 28 day part of the menstural cycle.
- Heart disease, heart attacks and stomach ulcers are all 2 to 3 times as common in long-term shift workers.
- Conditions such as diabetes are more difficult to control.
- Some shift rotations are worse than others; e.g. 12 hour shifts and highly variable shift patterns.
- There is no perfect shift pattern; larks and owls have different requirements.
- When day and night shifts are permanent, staff turnover drops and accident levels fall.
- Implications for childcare facilities for shift workers.
- Junior doctors in hospitals can be on duty for 36 hours (48 at weekends). [1994]
- Modern treatment means earlier treatment in emergency and accident units, and less opportunity for rest periods when on call.
- One hospital is trying 24 hours on, 24 hours off for both consultants and junior doctors in E&A unit. [1994. Conclusions? Not traced any report on effectiveness.]
- The most extreme shift patterns are in aviation; e.g. 12 day transatlantic schedule. Sleeping in the cockpit not allowed in USA but UK and European regulations allow planned naps. NASA experimented with 40 min rest period in rotation for aircrew and found crew were more alert and less prone to 'microsleeps'.
BBC2 TV Horizon programme Against the clock, broadcast 2 April 1994
