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Asthma action plans recommend classifying respiratory status as green, yellow or red, depending on symptoms and peak expiratory flow. The green zone is 80% of the patient's usual peak flow and above; yellow is 50-80% and red is less than 50%. The usual (asymptomatic) peak flow should be measured for the individual patient, but can be estimated based on patient height (Hsu et al. (1979) Ventilatory functions of normal children and young adults—Mexican-American, white and black. I. Spirometry. Journal of Pediatrics 95:14-23).

Remove technical details.

Set the sex with sex=male or sex=female. If neither is specified, then the percentiles are averaged.

The usual peak flow level is set with pf=nnn. If you want to use the patient height to estimate the predicted peak flow, use height=hhh. If no height is given, the CDC growth charts are used for the 50^th percentile for height for the patient's age at the time of the last data point (or the current date if no data are present).

Hsu et al.'s paper measured pulmonary function separately for white, black, and Mexican students in Texas schools in 1976. The differences in the means between ethnicities was statistically significant (p < 0.01 for the largest differences by my back-of-the-envelope Student's t test) but likely not clinically important. The differences are about 10%, while the standard deviation is about 20%, so individual variability outweighs inter-ethnicity variablility. Nonetheless, the program can use the ethnicity-specific factors with the parameters ethnicity=white, ethnicity=african-american, or ethnicity=hispanic. I am aware that "Hispanic" is a misnomer here; the paper studied only Mexican-Americans, but that is the nomenclature used by the Riley Kidometer and seems to be useful.

If you want to use a population distribution of ethnicity, use, e.g., ethnicity[white]=0.7&ethnicity[african-american]=0.2&ethnicity[hispanic]=0.1 and the program will average the predicted peak flow appropriately. If no ethniicty is given, the default is ethnicity[white]=0.74&ethnicity[african-american]=0.13&ethnicity[hispanic]=0.13, taken from the 2000 US census.

Examples

/webservices/pf.png?birth=9 years ago&time-min=1 week ago&time-max=tomorrow&pf=200&date[]=2 days ago&data[]=200&date[]=yesterday&data[]=150&date[]=today&data[]=100

Plots the graph for a 9 year old (also showing the flexibility of strtotime in describing dates) with known personal best peak flow and a deteriorating course.

/webservices/pf.png?birth=9 years ago&time-min=1 week ago&time-max=tomorrow&height=141&date[]=2 days ago&data[]=200&date[]=yesterday&data[]=150&date[]=today&data[]=100

Same graph, but with using a measured height to predict peak flow.

/webservices/pf.png?birth=9 years ago&time-min=1 week ago&time-max=tomorrow&date[]=2 days ago&data[]=200&date[]=yesterday&data[]=150&date[]=today&data[]=100

Same graph, but with using 50^th percentile height to predict peak flow.