**5. Associative relationships of microclimate and physical health**

#### **5.1 Heart rate**

**Figure 3** shows the Shapley Summary Plot of the associations of microclimate with the variable 'heart rate'.

From **Figure 3**, the variable 'heart rate' is most strongly associated with the variable 'carbon dioxide concentration' (feature importance of 0.15), followed by the variable 'sound' (feature importance of 0.14) and by three variables which affects heart rate co-equally (feature importance of 0.08), namely 'ambient temperature', 'dust concentration' and 'air pressure'. From the above Shapley Summary Plot, the lower the carbon dioxide concentration, the lower the heart rate. As for sound, the higher the sound in the surrounding microclimate is, the higher the heart rate level. Similarly, the higher the pressure and dust concentration are, the higher the heart rate level while heart rate value decreases when ambient temperature increases. An interesting observation is that heart rate dropped from 5 pm onward.

#### **5.2 Heart rate variability (rMSSD)**

In the context of heart rate variability, rMSSD refers to the physiological phenomenon of variation in the time interval between heartbeats. **Figure 4** shows the Shapley Summary Plot of the associations of microclimate with this variable.

From **Figure 4**, the variable 'root mean square of successive beat-to-beat interval differences' ('rMSSD') is most strongly associated with the variable 'sound' (feature

#### **Figure 3.**

*Shapley summary plot of microclimatic factors and heart rate.*

im-portance of 0.46), followed by the variable 'dust concentration' (feature importance of 0.09), then co-equally (feature importance of 0.07) by the variables 'ambient temperature' and 'wind direction'. From the above Shapley Summary Plot, the higher sound is, the lower the rMSSD is. The higher dust concentration is, the lower the rMSSD. Similarly, the higher the ambient temperature and the more westerly the wind, the lower the rMSSD.

#### **5.3 Skin temperature at the wrist**

**Figure 5** shows the Shapley Summary Plot of the associations of microclimate with the variable 'skin temperature at the wrist'.

From **Figure 5**, the variable 'skin temperature at the wrist' is most strongly associated with the variable 'sound' (feature importance of 0.21), followed by the variable 'dust concentration' (feature importance of 0.13) and the variable 'ambient

*The Life2 Well Project: Investigating the Relationship between Physiological Stress… DOI: http://dx.doi.org/10.5772/intechopen.107493*

#### **Figure 4.**

*Shapley summary plot of microclimatic factors and rMSSD.*

temperature' (feature importance of 0.12). From the above Shapley Summary Plot, the higher sound is, the higher the skin temperature. In attempting to interpret this, one might consider sound to be a proxy indicator of the nature of one's immediate environment, which – in turn – may have attributes which results in physiological responses, including with respect to skin temperature. The lower amount of dust concentration present is, the higher the skin temperature. The higher ambient temperature is, the higher the skin temperature but it rises at a lower rate.

#### **5.4 Self-reported physical state**

**Figure 6** shows the Shapley Summary Plot of the associations of microclimate with the variable 'self-reported physical state'.

From **Figure 6**, the variable 'self-reported physical state' is most strongly associated with the variable 'sound' (feature importance of 0.17), followed by the variable 'carbon dioxide concentration' (feature importance of 0.15) and by the variable 'dust

#### **Figure 5.**

*Shapley summary plot of microclimatic factors and skin temperature.*

concentration' (feature importance of 0.13). From the above Shapley Summary Plot, the higher level of sound, the higher the value of self-reported physical state. Similarly, the higher carbon dioxide concentration is, the higher the value of self-reported physical state. Finally, as dust concentration decreases, the value of self-reported physical state increases.
