40
Marine Mammal Physiology: Requisites for Ocean Living
The assumption that Mb concentration is constant throughout a muscle or among
different muscles may also be incorrect. In several studies of seals, Mb concentrations
have been shown to differ: (1) between individual muscles, (2) in the location within a
single muscle, and (3) with the season of the year (Neshumova et al. 1983; Neshumova
and Cherepanova 1984; Petrov and Shoshenko 1987; Polasek and Davis 2001; Polasek et al.
2006). However, at least in the Baikal seal (Phoca sibirica), the mean Mb concentration of
all muscles was not that different from the Mb content of the primary locomotory muscle
(Neshumova and Cherepanova 1984). Thus, the use of Mb concentration measurements
from a single locomotory muscle should provide a reasonable estimate of muscle O 2 stores.
2.3.4 Measuring heart rate
Heart rates of diving animals are usually determined from the electrocardiogram (ECG)
signal. The typical ECG signal that is associated with a heartbeat consists of a P wave
(atrial contraction), QRS complex (ventricular contraction), and T wave (ventricular relaxation). Beat-to-beat heart rates are usually calculated from the time intervals between successive R waves (the R–R interval). There have been two common types of recorders used
in heart rate studies of marine mammals (Ponganis 2007). The first technique consists of
an electronic R wave detector that recognizes the R wave based on its height, width, and
polarity. The second technique is the actual recording of the ECG signal.
The R-wave detector is usually programmed to count the number of detected R waves
over a given time interval, and then store that value in memory. Such recorders provide a
record of heart rate at fixed intervals throughout the dive. The advantages of such recorders are that signal processing is automatic, memory usage is minimal, and heart rates can
be recorded over long time periods. Disadvantages are that potential error due to artifact
is unrecognized and beat-to-beat heart rates are not recorded.
In contrast, an ECG recorder provides a continuous ECG record, from which each R–R
interval can be calculated so that the instantaneous heart rate profiles can be constructed.
The advantages of this technique are that accurate R wave detection can be verified, beatto-beat changes in heart rate are recorded, and variability in heart rate profiles can be
assessed. The disadvantages include memory storage (typically the ECG is recorded at
50–100 Hz), the need for peak detection programs to recognize the R waves and calculate
the heart rate, and the time to process the ECG records with such programs.
The challenge in collecting heart rate data is secure placement of the ECG electrodes in
the proper position so that a good signal is detected and there is no muscle or movement
artifact in the record. This varies with species. Both surface and subcutaneous electrodes
have been used in marine mammals (Hill et al. 1987; Williams et al. 1992; Thompson and
Fedak 1993; Andrews et al. 1997; Hindle et al. 2010; Davis and Williams 2012; McDonald
and Ponganis 2014). Surface electrodes have usually been attached with epoxy glues in
pinnipeds and with suction cups in cetaceans.
2.3.5 Measuring blood lactate to determine the ADL
Documentation of blood lactate concentrations to determine the ADL of a given species
has required vascular access to the animal to obtain blood samples and the subsequent
analysis of those samples for lactate content. The ability to reliably obtain blood samples
in the post-dive period without disturbing the animal has been most critical and difficult
to achieve. Such studies have been carried out under two conditions—with trained or captive animals, or with wild animals at an isolated dive hole to which they must return in
Marine Mammal Physiology: Requisites for Ocean Living
The assumption that Mb concentration is constant throughout a muscle or among
different muscles may also be incorrect. In several studies of seals, Mb concentrations
have been shown to differ: (1) between individual muscles, (2) in the location within a
single muscle, and (3) with the season of the year (Neshumova et al. 1983; Neshumova
and Cherepanova 1984; Petrov and Shoshenko 1987; Polasek and Davis 2001; Polasek et al.
2006). However, at least in the Baikal seal (Phoca sibirica), the mean Mb concentration of
all muscles was not that different from the Mb content of the primary locomotory muscle
(Neshumova and Cherepanova 1984). Thus, the use of Mb concentration measurements
from a single locomotory muscle should provide a reasonable estimate of muscle O 2 stores.
2.3.4 Measuring heart rate
Heart rates of diving animals are usually determined from the electrocardiogram (ECG)
signal. The typical ECG signal that is associated with a heartbeat consists of a P wave
(atrial contraction), QRS complex (ventricular contraction), and T wave (ventricular relaxation). Beat-to-beat heart rates are usually calculated from the time intervals between successive R waves (the R–R interval). There have been two common types of recorders used
in heart rate studies of marine mammals (Ponganis 2007). The first technique consists of
an electronic R wave detector that recognizes the R wave based on its height, width, and
polarity. The second technique is the actual recording of the ECG signal.
The R-wave detector is usually programmed to count the number of detected R waves
over a given time interval, and then store that value in memory. Such recorders provide a
record of heart rate at fixed intervals throughout the dive. The advantages of such recorders are that signal processing is automatic, memory usage is minimal, and heart rates can
be recorded over long time periods. Disadvantages are that potential error due to artifact
is unrecognized and beat-to-beat heart rates are not recorded.
In contrast, an ECG recorder provides a continuous ECG record, from which each R–R
interval can be calculated so that the instantaneous heart rate profiles can be constructed.
The advantages of this technique are that accurate R wave detection can be verified, beatto-beat changes in heart rate are recorded, and variability in heart rate profiles can be
assessed. The disadvantages include memory storage (typically the ECG is recorded at
50–100 Hz), the need for peak detection programs to recognize the R waves and calculate
the heart rate, and the time to process the ECG records with such programs.
The challenge in collecting heart rate data is secure placement of the ECG electrodes in
the proper position so that a good signal is detected and there is no muscle or movement
artifact in the record. This varies with species. Both surface and subcutaneous electrodes
have been used in marine mammals (Hill et al. 1987; Williams et al. 1992; Thompson and
Fedak 1993; Andrews et al. 1997; Hindle et al. 2010; Davis and Williams 2012; McDonald
and Ponganis 2014). Surface electrodes have usually been attached with epoxy glues in
pinnipeds and with suction cups in cetaceans.
2.3.5 Measuring blood lactate to determine the ADL
Documentation of blood lactate concentrations to determine the ADL of a given species
has required vascular access to the animal to obtain blood samples and the subsequent
analysis of those samples for lactate content. The ability to reliably obtain blood samples
in the post-dive period without disturbing the animal has been most critical and difficult
to achieve. Such studies have been carried out under two conditions—with trained or captive animals, or with wild animals at an isolated dive hole to which they must return in