Acta Otolaryngol 79: 133-139, 1975
THE INFLUENCE OF VARYING AIR HUMIDITY ON MUCOCILIARY ACTIVITY
U. Mercke From the E N T Department, University Hospital, Lund, Sweden
Acta Otolaryngol Downloaded from informahealthcare.com by Nyu Medical Center on 06/02/15 For personal use only.
(Received April 1, 1974)
Abstract. The influence of varying humidity levels in the air surrounding the mucous membrane of rabbit tracheae has been investigated in vitro at 34"C, 37°C and 40°C. The following results were obtained: (I) The average mucociliary wave frequency was linearly reduced following decreasing levels of relative humidity (r.h.) from 90 % to 20 %. (2) A temperature of 40°C was more detrimental to the mucociliary function than that of 34°C and 37°C (body temperature) a t decreasing levels of r.h. ( 3 ) At decreasing levels of r.h. the duration of experiments with preservation in recordable activity ("mucociliary survival time") was significantly shorter ( p 0.05) between 50 "4 and 40 % r.h. than between 60 % and 50 "b r.h. 4
The mucociliary activity of the mucous membrane in the mammalian respiratory tract may be influenced by many different factors such as temperature (von Gebhardt, 1909; Proetz, 1 9 3 4 ~ ;Dalhamn, 1956, 1960; Hill, 1957; Iravani, 1967; Tanaka, 1967), relative humidity (Florey etal., 1932; Proetz, 1933, 39346, 1944; Cralley, 1942a; Dalhamn, 1956; Toremalm, 1961; Ballenger & Orr, 1963; Ewert, 1965), mechanical trauma (Umeda, 1929; Proetz, 1933; Hill, 1957; Iravani, 1967), inhaled gases and particles (Cralley, 19426; Dalhamn, 1956; Dalhamn & Rhodin, 1956; Kensler & Battista, 1966) air ions (Krueger & Smith, 1957, 1958; Andersen, 1971) and ionizing irradiation (Fujiwara et al., 1972). However, under normal physiological conditions the temperature and humidity of the inThis investigation has been supported by grants from the Swedish Medical Research Council, Project No B7314X-3897-01 and Project No B74-61P-4282-01.
spired air are especially responsible for the maintenance of mucociliary activity (Proetz, 1953; Rivera, 1962). The influence of the temperature parameter in the range 20°C-40°C on the rabbit trachea under in vitro conditions and at a relative humidity above 90% has been described in a recent publication (Mercke et al., 1974b). The importance of an adequate degree of humidity for the maintenance of mucociliary activity has been pointed out in many publications especially those dealing with anaesthesiological problems (Friedman, 1955; Burton, 1962; Graff & Benson, 1969; Chamney, 1969). Specific data have only occasionally been published regarding the lower limit for affecting mucociliary activity (Dalhamn, 1956; Ewert, 1965). A systematic investigation on mammals regarding the influence of varying humidity on the mucociliary wave frequency at different temperature levels has not been found in the literature. Such an investigation under in vitro conditions is of basic interest for further experimental research in this field. The aim of the present investigation has therefore been to record and evaluate the mucociliary wave frequency of the respiratory tract in vitro in rabbits during exposure to varying humidity of the surrounding air. The following questions are considered: 1. How does a reduction of relative humidity (r.h.) influence the mucociliary activity at body temperature (37°C) t- 3"C? Acta Otolaryngol 79
134 U. Mercke flowmeter
I,!
Acta Otolaryngol Downloaded from informahealthcare.com by Nyu Medical Center on 06/02/15 For personal use only.
autotransformer
heater I
I: I
saturator
Psychrometer
--
Fig. 1. The experimental chamber provided with a special arrangement for regulating the temperature and relative humidity of the air-flow around the tracheal specimen.
2. For how long time is it possible t o work experimentally on tracheal specimens with retained mucociliary activity at different levels of reduced relative humidity at the above mentioned temperatures? METHOD A ND MATERIAL The experimental apparatus consists of a cold light source, a binocular microscope, a photomultiplier with amplifier, a frequency filter and an ink-writer, which have been described in detail previously (Mercke et al., 1 9 7 4 ~ ) . The experimental chamber described by Hikansson & Toremalm (1965) has been redesigned to make possible regulation and registration of temperature and r.h. (Fig. 1). An air stream is led to a saturator where it is heated to the desired temperature and moistened by bubbling through Ringer solution. Another air stream is led to a heater which reduces its humidity and raises its temperature to the same as Acta Otolaryngol79
that in the saturator. Both air streams are then mixed and fed into that part of the experimental chamber where the tracheal specimen is mounted. A thermocouple and a psychrometer (ELLAB type KC 1) are placed close to the tracheal mucous membrane to record the temperature and the humidity in the chamber. By mixing the air streams any desired humidity can be obtained in the experimental chamber. With the exception of the space where the tracheal specimen is mounted the experimental chamber contains circulating water which is kept at a constant temperature with the aid of a precision thermostate. The air from the saturator and the heater has the same temperature as the water supply of the experimental chamber. Rabbits were used as experimental animals. They were killed by a blow on the head. The tracheae were prepared rapidly and suspended between two perspex tubes in the experimental chamber. The mucous membrane was observed from above through a hole in the upwards directed pars membranacea. Two experimental series have been carried out: 1. Starting from 90%, the r.h. has been lowered 10 % at a time down to 20 %. The specimens have been exposed to each level for 30 min during which two recordings each at 30-60 sec were made. The experiments have been performed at the following constant temperature levels: 34°C (4 rabbits), 37°C (6 rabbits) and 40°C (7 rabbits). The duration has been 240 min. 2. The maximum exposure time or “mucociliary survival time” has been estimated at constant r.h. and temperatures. At each of the three temperature levels, the humidity levels 60 % (5, 7 and 9 rabbits respectively), 50% (4, 4 and 4 rabbits respectively) and 40 % (4, 4 and 4 rabbits respectively) have been investigated. The duration of the experiments has been limited to 120 min. RESULTS Rabbit tracheae exposed to decreasing relative humidity levels In Figs. 2, 3 and 4 the recorded mucociliary wave frequency (Table I) has been plotted
Air humidity and mucociliary activity 135
I
70%
40%
60%
60%
30%
40%
1200
,000.
..
600.
600.
*
.
400.
200.
Acta Otolaryngol Downloaded from informahealthcare.com by Nyu Medical Center on 06/02/15 For personal use only.
__
-
*
20%
30%
11
1400.
180
210
240
Time m i n t
Fig. 2. Diagram showing the mucociliary wave frequency at different degrees of relative humidity (%) during a period of 4 hours. Constant temperature 34°C.
against the successively decreasing humidity levels during 240 min and the time of recording. Firstly, it appears that the initial value of the wave frequency increases with increasing temperature, from 693 i56 waves/min at 34°C to 1 138131 waves/min at 40°C. Secondly, there is a tendency for the frequency to decrease following decreasing r.h. At 34°C the initial value of the wave frequency at 90% r.h. (693k56 waves/min) is reduced by approximately onethird at 30% r.h. (440 waves/min). This tendency to frequency reduction is also found at 37"C, and is even more accentuated at 40"C, where no specimen shows activity at 30% r.h. At all three temperature levels most cases of ceased wave movement can be found in the range between 60 % and 40 Yo r.h. 37OC
30%
30%
70%
Fig. 4 . Diagram showing the mucociliary wave frequency at different degrees of relative humidity ( % ) during a period of 4 hours. Constant temperature 40°C.
Fig. 5 illustrates the original records from one rabbit trachea at 37°C and 60'36, 50% and 40% r.h. These records are made with an interval of 30 min and show how the successive decrease of the r.h. finally is followed by ciliestasis. The average frequency at each humidity level is plotted against the respective humidity at Fig. 6A-C. The inclination coefficients ( k ) of the regression lines are 3.7 at 34"C, 3.1 at 37°C and 18.0 at 40°C (Fig. 6D). The smallest inclination coefficient belongs to the regression line for 37"C, i.e. the body temperature of the rabbit.
Rabbit tracheae exposed to constant humidity levels In this experimental series the tracheal specimens have been exposed to constant humidity
20%
Table I
..
- .. .*... .. .
Mean frequency (wavesimin) at
I
*
!
1
60
90
120
150
180
,
Fig. 3. Diagram showing the mucociliary wave frequency at different degrees of relative humidity (%) during a period of 4 hours. Constant temperature 37°C.
r.h. (%)
34°C
37°C
40°C
90 80 70 60 50 40 30
693 602 597 534 625 424 440 409
807 732 717 515 633 693 534 583
1138 991 850 445 509 288
20
-
Actu Otolaryngol 79
136 U. Mercke trequency
Relative humidity %
waves/min
882
60
Fig. 5. Typical records from one of the experiments in Fig. 3. Mucociliary wave frequency and pattern at 60%, 50% and 40 % relative humidity. Temperature 37°C. 0
40
Acta Otolaryngol Downloaded from informahealthcare.com by Nyu Medical Center on 06/02/15 For personal use only.
1 sec
levels at 60 %, 50 % and 40 % and three temperature levels during a maximum of 120 min. The “mucociliary survival time” has been noted (Fig. 7). The shorter survival at lower humidity levels is clearly shown at all three temperature levels investigated. i t can also be seen that the differences in “mucociliary survival time” for all three temperature levels are greater between 50% and 40% r.h. than between 60% and 50% r.h. In the former case this difference is found to be statistically significant ( p < 0.05) according to the Wilcoxon rank-sum-test. Frequency A (waves/min)
34nc
Frequency (waves/min)
6
370c
1200
1200
800 -
*Jc?it“
600
400:
’
*
THE INFLUENCE OF VARYING AIR HUMIDITY ON MUCOCILIARY ACTIVITY
U. Mercke From the E N T Department, University Hospital, Lund, Sweden
Acta Otolaryngol Downloaded from informahealthcare.com by Nyu Medical Center on 06/02/15 For personal use only.
(Received April 1, 1974)
Abstract. The influence of varying humidity levels in the air surrounding the mucous membrane of rabbit tracheae has been investigated in vitro at 34"C, 37°C and 40°C. The following results were obtained: (I) The average mucociliary wave frequency was linearly reduced following decreasing levels of relative humidity (r.h.) from 90 % to 20 %. (2) A temperature of 40°C was more detrimental to the mucociliary function than that of 34°C and 37°C (body temperature) a t decreasing levels of r.h. ( 3 ) At decreasing levels of r.h. the duration of experiments with preservation in recordable activity ("mucociliary survival time") was significantly shorter ( p 0.05) between 50 "4 and 40 % r.h. than between 60 % and 50 "b r.h. 4
The mucociliary activity of the mucous membrane in the mammalian respiratory tract may be influenced by many different factors such as temperature (von Gebhardt, 1909; Proetz, 1 9 3 4 ~ ;Dalhamn, 1956, 1960; Hill, 1957; Iravani, 1967; Tanaka, 1967), relative humidity (Florey etal., 1932; Proetz, 1933, 39346, 1944; Cralley, 1942a; Dalhamn, 1956; Toremalm, 1961; Ballenger & Orr, 1963; Ewert, 1965), mechanical trauma (Umeda, 1929; Proetz, 1933; Hill, 1957; Iravani, 1967), inhaled gases and particles (Cralley, 19426; Dalhamn, 1956; Dalhamn & Rhodin, 1956; Kensler & Battista, 1966) air ions (Krueger & Smith, 1957, 1958; Andersen, 1971) and ionizing irradiation (Fujiwara et al., 1972). However, under normal physiological conditions the temperature and humidity of the inThis investigation has been supported by grants from the Swedish Medical Research Council, Project No B7314X-3897-01 and Project No B74-61P-4282-01.
spired air are especially responsible for the maintenance of mucociliary activity (Proetz, 1953; Rivera, 1962). The influence of the temperature parameter in the range 20°C-40°C on the rabbit trachea under in vitro conditions and at a relative humidity above 90% has been described in a recent publication (Mercke et al., 1974b). The importance of an adequate degree of humidity for the maintenance of mucociliary activity has been pointed out in many publications especially those dealing with anaesthesiological problems (Friedman, 1955; Burton, 1962; Graff & Benson, 1969; Chamney, 1969). Specific data have only occasionally been published regarding the lower limit for affecting mucociliary activity (Dalhamn, 1956; Ewert, 1965). A systematic investigation on mammals regarding the influence of varying humidity on the mucociliary wave frequency at different temperature levels has not been found in the literature. Such an investigation under in vitro conditions is of basic interest for further experimental research in this field. The aim of the present investigation has therefore been to record and evaluate the mucociliary wave frequency of the respiratory tract in vitro in rabbits during exposure to varying humidity of the surrounding air. The following questions are considered: 1. How does a reduction of relative humidity (r.h.) influence the mucociliary activity at body temperature (37°C) t- 3"C? Acta Otolaryngol 79
134 U. Mercke flowmeter
I,!
Acta Otolaryngol Downloaded from informahealthcare.com by Nyu Medical Center on 06/02/15 For personal use only.
autotransformer
heater I
I: I
saturator
Psychrometer
--
Fig. 1. The experimental chamber provided with a special arrangement for regulating the temperature and relative humidity of the air-flow around the tracheal specimen.
2. For how long time is it possible t o work experimentally on tracheal specimens with retained mucociliary activity at different levels of reduced relative humidity at the above mentioned temperatures? METHOD A ND MATERIAL The experimental apparatus consists of a cold light source, a binocular microscope, a photomultiplier with amplifier, a frequency filter and an ink-writer, which have been described in detail previously (Mercke et al., 1 9 7 4 ~ ) . The experimental chamber described by Hikansson & Toremalm (1965) has been redesigned to make possible regulation and registration of temperature and r.h. (Fig. 1). An air stream is led to a saturator where it is heated to the desired temperature and moistened by bubbling through Ringer solution. Another air stream is led to a heater which reduces its humidity and raises its temperature to the same as Acta Otolaryngol79
that in the saturator. Both air streams are then mixed and fed into that part of the experimental chamber where the tracheal specimen is mounted. A thermocouple and a psychrometer (ELLAB type KC 1) are placed close to the tracheal mucous membrane to record the temperature and the humidity in the chamber. By mixing the air streams any desired humidity can be obtained in the experimental chamber. With the exception of the space where the tracheal specimen is mounted the experimental chamber contains circulating water which is kept at a constant temperature with the aid of a precision thermostate. The air from the saturator and the heater has the same temperature as the water supply of the experimental chamber. Rabbits were used as experimental animals. They were killed by a blow on the head. The tracheae were prepared rapidly and suspended between two perspex tubes in the experimental chamber. The mucous membrane was observed from above through a hole in the upwards directed pars membranacea. Two experimental series have been carried out: 1. Starting from 90%, the r.h. has been lowered 10 % at a time down to 20 %. The specimens have been exposed to each level for 30 min during which two recordings each at 30-60 sec were made. The experiments have been performed at the following constant temperature levels: 34°C (4 rabbits), 37°C (6 rabbits) and 40°C (7 rabbits). The duration has been 240 min. 2. The maximum exposure time or “mucociliary survival time” has been estimated at constant r.h. and temperatures. At each of the three temperature levels, the humidity levels 60 % (5, 7 and 9 rabbits respectively), 50% (4, 4 and 4 rabbits respectively) and 40 % (4, 4 and 4 rabbits respectively) have been investigated. The duration of the experiments has been limited to 120 min. RESULTS Rabbit tracheae exposed to decreasing relative humidity levels In Figs. 2, 3 and 4 the recorded mucociliary wave frequency (Table I) has been plotted
Air humidity and mucociliary activity 135
I
70%
40%
60%
60%
30%
40%
1200
,000.
..
600.
600.
*
.
400.
200.
Acta Otolaryngol Downloaded from informahealthcare.com by Nyu Medical Center on 06/02/15 For personal use only.
__
-
*
20%
30%
11
1400.
180
210
240
Time m i n t
Fig. 2. Diagram showing the mucociliary wave frequency at different degrees of relative humidity (%) during a period of 4 hours. Constant temperature 34°C.
against the successively decreasing humidity levels during 240 min and the time of recording. Firstly, it appears that the initial value of the wave frequency increases with increasing temperature, from 693 i56 waves/min at 34°C to 1 138131 waves/min at 40°C. Secondly, there is a tendency for the frequency to decrease following decreasing r.h. At 34°C the initial value of the wave frequency at 90% r.h. (693k56 waves/min) is reduced by approximately onethird at 30% r.h. (440 waves/min). This tendency to frequency reduction is also found at 37"C, and is even more accentuated at 40"C, where no specimen shows activity at 30% r.h. At all three temperature levels most cases of ceased wave movement can be found in the range between 60 % and 40 Yo r.h. 37OC
30%
30%
70%
Fig. 4 . Diagram showing the mucociliary wave frequency at different degrees of relative humidity ( % ) during a period of 4 hours. Constant temperature 40°C.
Fig. 5 illustrates the original records from one rabbit trachea at 37°C and 60'36, 50% and 40% r.h. These records are made with an interval of 30 min and show how the successive decrease of the r.h. finally is followed by ciliestasis. The average frequency at each humidity level is plotted against the respective humidity at Fig. 6A-C. The inclination coefficients ( k ) of the regression lines are 3.7 at 34"C, 3.1 at 37°C and 18.0 at 40°C (Fig. 6D). The smallest inclination coefficient belongs to the regression line for 37"C, i.e. the body temperature of the rabbit.
Rabbit tracheae exposed to constant humidity levels In this experimental series the tracheal specimens have been exposed to constant humidity
20%
Table I
..
- .. .*... .. .
Mean frequency (wavesimin) at
I
*
!
1
60
90
120
150
180
,
Fig. 3. Diagram showing the mucociliary wave frequency at different degrees of relative humidity (%) during a period of 4 hours. Constant temperature 37°C.
r.h. (%)
34°C
37°C
40°C
90 80 70 60 50 40 30
693 602 597 534 625 424 440 409
807 732 717 515 633 693 534 583
1138 991 850 445 509 288
20
-
Actu Otolaryngol 79
136 U. Mercke trequency
Relative humidity %
waves/min
882
60
Fig. 5. Typical records from one of the experiments in Fig. 3. Mucociliary wave frequency and pattern at 60%, 50% and 40 % relative humidity. Temperature 37°C. 0
40
Acta Otolaryngol Downloaded from informahealthcare.com by Nyu Medical Center on 06/02/15 For personal use only.
1 sec
levels at 60 %, 50 % and 40 % and three temperature levels during a maximum of 120 min. The “mucociliary survival time” has been noted (Fig. 7). The shorter survival at lower humidity levels is clearly shown at all three temperature levels investigated. i t can also be seen that the differences in “mucociliary survival time” for all three temperature levels are greater between 50% and 40% r.h. than between 60% and 50% r.h. In the former case this difference is found to be statistically significant ( p < 0.05) according to the Wilcoxon rank-sum-test. Frequency A (waves/min)
34nc
Frequency (waves/min)
6
370c
1200
1200
800 -
*Jc?it“
600
400:
’
*
