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PEAK EXPIRATORY FLOW RATE

Pooja Mehta

Family Physician, Vidyanagari, Mumbai, 400 098.

PEFR - peak expiratory flow rate - The maximal airflow rate achieved while forcefully expelling air from the lungs, following maximal inspiration; expressed in litres/ min

Thus, peak expiratory flow is a measurement, which tells us whether bronchioles are in spasm and if yes, their severity.

Significance of measuring PEFR

- It is helpful in distinguishing between constrictive (TB, silicosis) and obstructive (asthma) lung disease.
- In asymptomatic cases, it may be the only means of diagnosis.
- Can point out specific trigger factors for asthma.
- Can help judge the response to medication.

Normal values

These depend on height, age and sex of an individual. Thus values are greater in tall people, adults and in men

Using PEFR in day-to-day practice

1. Every patientís baseline PEFR must be noted.
2. Judge how low is it as compared to expected value (even on days when the patient is asymptomatic).
3. Look for improvement after nebulisation/ treatment.
4. A reduction in more than 20% of a patientís baseline value signifies severity.
5. A PEFR of d signifies a critical stage. This patient must be hospitalized, otherwise he may go in respiratory failure.
6. Chronic cases may be asked to purchase there own Peak flow meters and asked to check it 3 times a day. (a Peak flow meter costs only Rs 600/-)

The PEFR of an individual should fall within a range of 20% on either side of his predicted normal value.

Can PEFR be increased if expiratory force is greatly increased?

No, this is not possible. You may ask why?

Expected PEFR in children
Male/ Female child - 5 to 15 yrsHeight (Mts.)
PEFR (lts/min)
0.90
92
0.95
108
1.00
124
1.05
147
1.10
169
1.15
192
1.20
215
1.25
238
1.30
260
1.35
283
1.40
306
1.45
329
1.50
351
1.55
374
1.60
397
1.65
420
1.70
442
1.75
465
1.80
488

 

Expected PEFR depending on height and age of a male
Male adult Ht (Age)
18/25 yrs
30
35
40
45
50
55
60
65
70
1.55 Mt
515 lts/min
502
489
477
463
451
438
425
412
399
1.60
534
520
508
495
482
469
456
443
430
417
1.65
552
539
526
513
501
487
475
462
449
436
1.70
570
558
544
532
519
506
493
480
467
454
1.75
589
576
563
550
537
525
511
499
486
473
1.80
607
694
582
568
556
543
530
517
504
491
1.85
625
613
600
587
574
561
548
535
522
510
1.90
644
631
618
606
592
580
567
554
541
528
1.95
663
649
637
624
611
598
585
572
559
546

 

Expected PEFR depending on height and age of a female
Female adult Ht (Age)
18/25
30
35
40
45
50
55
60
65
70
1.45
367
358
349
340
331
322
313
304
295
286
1.50
383
374
365
356
347
338
329
320
311
302
1.55
400
391
382
373
364
355
346
337
328
319
1.60
416
407
398
389
380
371
362
353
344
335
1.65
433
424
415
406
397
388
379
370
361
352
1.70
449
440
431
422
413
404
395
386
377
368
1.75
466
457
448
439
430
421
412
403
394
385
1.80
482
473
464
455
446
437
428
419
410
401

Suppose external pressure is applied to the airways; say due to compression of chest cage- this gets distributed equally to alveoli and the bronchioles, thus compressing them. Alveolar air is forced out into the bronchioles, which being partially collapsed inhibit airflow. If this pressure is increased the bronchioles collapse completely and hence any further increase in expiratory flow is not possible.



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