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Effects of Gestational and Postnatal Exposure to Chronic Intermittent Hypoxia on Diaphragm Muscle Contractile Function in the Rat.

McDonald FB, Dempsey EM, O'Halloran KD - Front Physiol (2016)

Bottom Line: Alterations to the supply of oxygen during early life presents a profound stressor to physiological systems with aberrant remodeling that is often long-lasting.CIH affects respiratory control but there is a dearth of information concerning the effects of CIH on respiratory muscles, including the diaphragm-the major pump muscle of breathing.A mismatch in the force-generating capacity of the complementary muscle groups could have adverse consequences for the control of airway patency and respiratory homeostasis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, School of Medicine and Medical Science, University College Dublin Dublin, Ireland.

ABSTRACT
Alterations to the supply of oxygen during early life presents a profound stressor to physiological systems with aberrant remodeling that is often long-lasting. Chronic intermittent hypoxia (CIH) is a feature of apnea of prematurity, chronic lung disease, and sleep apnea. CIH affects respiratory control but there is a dearth of information concerning the effects of CIH on respiratory muscles, including the diaphragm-the major pump muscle of breathing. We investigated the effects of exposure to gestational CIH (gCIH) and postnatal CIH (pCIH) on diaphragm muscle function in male and female rats. CIH consisted of exposure in environmental chambers to 90 s of hypoxia reaching 5% O2 at nadir, once every 5 min, 8 h a day. Exposure to gCIH started within 24 h of identification of a copulation plug and continued until day 20 of gestation; animals were studied on postnatal day 22 or 42. For pCIH, pups were born in normoxia and within 24 h of delivery were exposed with dams to CIH for 3 weeks; animals were studied on postnatal day 22 or 42. Sham groups were exposed to normoxia in parallel. Following gas exposures, diaphragm muscle contractile, and endurance properties were examined ex vivo. Neither gCIH nor pCIH exposure had effects on diaphragm muscle force-generating capacity or endurance in either sex. Similarly, early life exposure to CIH did not affect muscle tolerance of severe hypoxic stress determined ex vivo. The findings contrast with our recent observation of upper airway dilator muscle weakness following exposure to pCIH. Thus, the present study suggests a relative resilience to hypoxic stress in diaphragm muscle. Co-ordinated activity of thoracic pump and upper airway dilator muscles is required for optimal control of upper airway caliber. A mismatch in the force-generating capacity of the complementary muscle groups could have adverse consequences for the control of airway patency and respiratory homeostasis.

No MeSH data available.


Related in: MedlinePlus

Effects of early life exposure to CIH on diaphragm muscle force in male and female rats under control conditions ex vivo. Data (mean ± SD) for diaphragm muscle specific force across a range of stimulation frequencies in male (left panels) and female rats (right panels) at postnatal day (P) 22 and P42 examined under control conditions ex vivo. Animals were exposed to sham (normoxia), gestational chronic intermittent hypoxia (gCIH), or postnatal CIH (pCIH). P-values following two-way RMANOVA (gas × stimulation frequency) are reported. Post-hoc tests revealed no significant effect of gCIH or pCIH exposure on diaphragm force. N-values for animals as per Table 1.
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Figure 1: Effects of early life exposure to CIH on diaphragm muscle force in male and female rats under control conditions ex vivo. Data (mean ± SD) for diaphragm muscle specific force across a range of stimulation frequencies in male (left panels) and female rats (right panels) at postnatal day (P) 22 and P42 examined under control conditions ex vivo. Animals were exposed to sham (normoxia), gestational chronic intermittent hypoxia (gCIH), or postnatal CIH (pCIH). P-values following two-way RMANOVA (gas × stimulation frequency) are reported. Post-hoc tests revealed no significant effect of gCIH or pCIH exposure on diaphragm force. N-values for animals as per Table 1.

Mentions: Two-way RMANOVA (gas × stimulus frequency) revealed the expected increase in force with increased frequency of stimulation in all groups (Figure 1). At P22, in both males and females, there was no gas effect. At P42 in male but not female rats, two-way RMANOVA (gas × stimulus frequency) revealed a gas effect (P = 0.04), however post-hoc tests at each frequency did not reveal significant differences between sham and CIH-exposed groups. Moreover, key properties of the force-frequency relationship (Hillslope and EF50) were not altered by exposure to CIH in either sex (Table 2). Thus, early life exposure to CIH had no effect on diaphragm force-generating capacity.


Effects of Gestational and Postnatal Exposure to Chronic Intermittent Hypoxia on Diaphragm Muscle Contractile Function in the Rat.

McDonald FB, Dempsey EM, O'Halloran KD - Front Physiol (2016)

Effects of early life exposure to CIH on diaphragm muscle force in male and female rats under control conditions ex vivo. Data (mean ± SD) for diaphragm muscle specific force across a range of stimulation frequencies in male (left panels) and female rats (right panels) at postnatal day (P) 22 and P42 examined under control conditions ex vivo. Animals were exposed to sham (normoxia), gestational chronic intermittent hypoxia (gCIH), or postnatal CIH (pCIH). P-values following two-way RMANOVA (gas × stimulation frequency) are reported. Post-hoc tests revealed no significant effect of gCIH or pCIH exposure on diaphragm force. N-values for animals as per Table 1.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940388&req=5

Figure 1: Effects of early life exposure to CIH on diaphragm muscle force in male and female rats under control conditions ex vivo. Data (mean ± SD) for diaphragm muscle specific force across a range of stimulation frequencies in male (left panels) and female rats (right panels) at postnatal day (P) 22 and P42 examined under control conditions ex vivo. Animals were exposed to sham (normoxia), gestational chronic intermittent hypoxia (gCIH), or postnatal CIH (pCIH). P-values following two-way RMANOVA (gas × stimulation frequency) are reported. Post-hoc tests revealed no significant effect of gCIH or pCIH exposure on diaphragm force. N-values for animals as per Table 1.
Mentions: Two-way RMANOVA (gas × stimulus frequency) revealed the expected increase in force with increased frequency of stimulation in all groups (Figure 1). At P22, in both males and females, there was no gas effect. At P42 in male but not female rats, two-way RMANOVA (gas × stimulus frequency) revealed a gas effect (P = 0.04), however post-hoc tests at each frequency did not reveal significant differences between sham and CIH-exposed groups. Moreover, key properties of the force-frequency relationship (Hillslope and EF50) were not altered by exposure to CIH in either sex (Table 2). Thus, early life exposure to CIH had no effect on diaphragm force-generating capacity.

Bottom Line: Alterations to the supply of oxygen during early life presents a profound stressor to physiological systems with aberrant remodeling that is often long-lasting.CIH affects respiratory control but there is a dearth of information concerning the effects of CIH on respiratory muscles, including the diaphragm-the major pump muscle of breathing.A mismatch in the force-generating capacity of the complementary muscle groups could have adverse consequences for the control of airway patency and respiratory homeostasis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, School of Medicine and Medical Science, University College Dublin Dublin, Ireland.

ABSTRACT
Alterations to the supply of oxygen during early life presents a profound stressor to physiological systems with aberrant remodeling that is often long-lasting. Chronic intermittent hypoxia (CIH) is a feature of apnea of prematurity, chronic lung disease, and sleep apnea. CIH affects respiratory control but there is a dearth of information concerning the effects of CIH on respiratory muscles, including the diaphragm-the major pump muscle of breathing. We investigated the effects of exposure to gestational CIH (gCIH) and postnatal CIH (pCIH) on diaphragm muscle function in male and female rats. CIH consisted of exposure in environmental chambers to 90 s of hypoxia reaching 5% O2 at nadir, once every 5 min, 8 h a day. Exposure to gCIH started within 24 h of identification of a copulation plug and continued until day 20 of gestation; animals were studied on postnatal day 22 or 42. For pCIH, pups were born in normoxia and within 24 h of delivery were exposed with dams to CIH for 3 weeks; animals were studied on postnatal day 22 or 42. Sham groups were exposed to normoxia in parallel. Following gas exposures, diaphragm muscle contractile, and endurance properties were examined ex vivo. Neither gCIH nor pCIH exposure had effects on diaphragm muscle force-generating capacity or endurance in either sex. Similarly, early life exposure to CIH did not affect muscle tolerance of severe hypoxic stress determined ex vivo. The findings contrast with our recent observation of upper airway dilator muscle weakness following exposure to pCIH. Thus, the present study suggests a relative resilience to hypoxic stress in diaphragm muscle. Co-ordinated activity of thoracic pump and upper airway dilator muscles is required for optimal control of upper airway caliber. A mismatch in the force-generating capacity of the complementary muscle groups could have adverse consequences for the control of airway patency and respiratory homeostasis.

No MeSH data available.


Related in: MedlinePlus